SEMINAR REPORT ON

PEROVSKITES, ITS TYPES AND APPLICATIONS

Submitted to Department of Physics

Chandigarh University, Gharuan

In the partial fulfillment of the degree of MASTER OF SCIENCE

IN PHYSICS

Under the guidance of-: Dr.Merry Gupta ASSISTANT PROFESSOR

Submitted by-: VARUNJOT KAUR (19MSP1031)

UNIVERSITY INSTITUTE OF SCIENCES CHANDIGARH UNIVERSITY, GHARAUN, PUNJAB, INDIA

1

CONTENTS

SR.NO. DESCRIPTION PAGE NO.01. ABSTRACT 03

02.

2.1

2.2

INTRODUCTION TO PEROVSKITES

DEFINITION AND EXAMPLES OF PEROVSKITES

FORMATION OF PEROVSKITES(FABRICATION OF PEROVSKITES)

04-06

04-05

05-06

03.STRUCTURE OF PEROVSKITES

07-08

04. TYPES OF PEROVSKITES 09-1105. IMPORTANT FEATURES OF

PEROVSKITES 12

06. PROPERTIES OF PEROVSKITES

13-15

07.

7.17.27.37.47.57.67.7

APPLICATIONS OF PEROVSKITES

PEROVSKITE SOLAR CELLSGas sensorsGlucose sensorNeurotransmitter sensorSolid oxide fuel cellsCatalystLASER

16-20

17-181818-1919191919-20

08. ADVANTAGES AND DISADVANTAGES OF USING PEROVSKITES

21

09. FUTURE OF PEROVSKITES 2210. CONCLUSION or

(summary)23

11. References 242

12. List of figures 25

3

01. ABSTRACT

As we know that in last few years perovskites are being considered as a big part

or a point of attention. Perovskite solar cells (PSCs) have shown a great potential

in the field of alternative energy due to their superior performance and processing

compatibility. However, prior to commercialization, a major drawback of poor

stability needs to be addressed imperatively. Recently, mixing 3D and 2D

perovskite as active layer is a promising strategy for blocking water and oxygen

to increase stability, as well as mitigating the effect of insulated spacer in bulk to

strengthen charge migration .The rapid improvement of perovskite solar cells has

made them the rising star of the photovoltaics world and of huge interest to the

academic community. Since their operational methods are still relatively new.

So, there is great opportunity for further research into the basic physics and

chemistry around perovskites. Crystallization in ceramics is usually considered to

be a problem in the glass industry. However, controlled crystallization of

ceramics is a necessary requirement in the development of perovskites with its

useful properties. This article presents an overview of various aspects of

perovskites where crystallization is either considered to be either advantageous or

problematic. Perovskites represent an exciting playground for physicists,

chemists and material scientists. This study is useful to explore the feasibility of

calcium titanium oxide.

4

Introduction

2.1 DEFINATION AND EXAMPLES OF PEROVSKITES

Perovskite analogues to natural mineral is a synthetic compound which have an orthorhombic crystal

structure with the same structural formula as CaTiO3. Due to their structural properties, these types of

materials have shown potential applications in the field of optoelectronics and photonics. These are being

emerged as the most promising and efficient materials with low cost for many of its applications.

True perovskite is composed of calcium, titanium and oxygen in the form CaTiO3. Perovskites take their

name from the mineral, which was first discovered in the Ural Mountains of Russia by Gustav Rose in 1839

and is named after Russian mineralogist L. A. Perkoski (1792–1856) [1].

Generally, the mineral of perovskites is colored because of the presence of impurities but perovskites are

colorless and diamagnetic solids. The general chemical formula for perovskite compounds is ABX3, where

'A' and 'B' are two cations of very different sizes, and X is an anion that bonds to both. The 'A' atoms are

larger than the 'B' atoms. [2]

The perovskite lattice arrangement is demonstrated below in figure 2.1

Perovskites can be represented in many ways but the simplest way to think about structure of perovskite is

as large molecular cation (positively charged) of type A in the Centre of a cube. The corners of the cube are

then occupied by atoms B (also positively charged cations) and the faces of the cube are occupied by a

smaller atom X with negative charge (anion). To absorb light the perovskite structure uses compounds and

stoichiometry. Researchers remain uncertain why positive and negative charges produced by photoexcitation

in these types of cells reach their electrodes so well. Yet the significant rate of development caused PV

scientists in industry and academia who operated other cells to switch to perovskites or at minimum enhance

the issue to their first list. Material scientists have shown enormous interest in perovskite because it is

abundantly available in nature. [3]

Fig 2.2 – perovskite mineral structure5

Researchers also found that the exploration of superconductivity, magneto resistance, ionic conductivity,

and gathering of dielectric properties are significant in telecommunication and microelectronics. Perovskite

mineral has the capacity to absorb light and it utilizes less than 1 μm of material to seizure the similar

quantity of sunlight compared to other solar cells. Perovskite is a semiconductor, which is used to transport

the electric charge whenever the light hits the material. In the United Kingdom, Oxford University physicists

have found that the perovskite has been used as the replacement for thin-film solar cells A cell with the

perovskite crystal structure usually consists of an organic group tin or lead and a halogen is called PSC .[3]

Methylammonium lead halide is the most prominent and widely used perovskite cells. The first structure of

perovskite Solar Cell is based on the dye-sensitized solar cell where the TiO2 layer is placed and the organic

materials are deposited over the layers where the perovskite will act only as the light absorbent and later it

will also transport the charge carriers for the mobility of electrons. Perovskites were first successfully used

in solid-state solar cells in 2012, and since then most cells have used the following combination of materials

in the usual perovskite form ABX3:

A = An organic cation - methylammonium (CH3NH3+) or formamidinium (NH2CHNH2

+)

B = A big inorganic cation - usually lead (II) (Pb2+)

X3= A slightly smaller halogen anion – usually chloride (Cl-) or iodide (I-) [4]

Some of the basic Examples of perovskites are LEAD TITANATE, BISMUTH FERRITE, LANTHANUM

YTTERBIUM OXIDE, SILICATE PEROVSKITE, LANTHANUM MANGANITE, YTTRIUM

ALUMINUM PEROVSKITE (YAP). Out of these strontium titanite is the most widely used

perovskite(SrTiO3). It has melting point of about 2353.15 kelvin. At room temperature, it is a

centrosymmetric paraelectric material with a perovskite structure. At low temperatures it approaches a

ferroelectric phase with a very large dielectric constant ~104 but remains paraelectric down to the lowest

temperatures which are measured as a result of quantum fluctuations which further makes it quantum

paraelectric. At room temperature it exists in cubic form but transforms into tetragonal structure at

temperature less than 105 kelvin. Due to its temperature variant nature it is used in tuneable HTS (high

temperature superconducting) microwave filters. SrTiO3 has an indirect band gap of 3.25 eV and a direct gap

of 3.75 eV. Synthetic strontium titanite has a very large dielectric constant (300) at room temperature and 6

low electric field. It has a specific resistivity of over 109 Ω-cm for very pure crystals. It is also used in high-

voltage capacitors. At high electron densities strontium titanite becomes superconducting below 0.35 K and

was the first insulator and oxide discovered to be superconductive. It is used as a diamond simulant.

Moreover, its cubic structure and high dispersion have made the synthetic strontium titanite a major part for

simulating diamond.[5]

Fig – 2.3 strontium titanite

Eventually, in 1955 Strontium titanite was in competition with synthetic rutile ("Titania") which had the

advantage of lacking the unfortunate yellow tinge and strong birefringence inherent to the latter material.

While it was softer, it was significantly closer to diamond in likeness. However, both had the same dis-

advantages of being eclipsed by the creation of "better" simulants using yttrium aluminium garnet (YAG),

gadolinium gallium garnet (GGG) and finally using ultimate simulant in terms of diamond-likeness and

cost-effectiveness. Strontium titanite is still manufactured and periodically encountered in jewellery as it is

one of the costliest forms of diamond simulants, and due to its rare nature collectors pay a very large

premium. As a diamond simulant, strontium titanite is the most deceptive when mingled with melee and is

used as the base material for a doublet stone. Gemmologists distinguished strontium titanite from diamond

using microscope because of these properties: the former's softness, surface abrasion, excess dispersion and

occasional gas bubbles which are remnants of synthesis. Doublets can be detected by a joining a line at the

waist of the stone and flattened air bubbles are visible within the stone at the point of bonding. It is Used in

radioisotope thermoelectric generators Due to its high melting point and insolubility. Strontium titanite is

also being used as a strontium-90-containing material in radioisotope thermoelectric generators, such as the

US Sentinel and Soviet Beta-M series.[4]

2.2 Formation of perovskites (fabrication of perovskites)

Perovskites can be incorporated very easily into a standard other thin film architecture. The first perovskite solar cells were based on solid state dye-sensitized solar cells (DSSCs) which are used a mesoporous TiO 2

scaffold. Since Many cells follow this or used Al2O3 scaffold in a ‘meso-super structured’ architecture. But the high temperature steps required for manufacturing and UV instability of TiO2, leds to introduction of a ‘planar’ architecture like other thin-film cells. After several years of lagging behind mesoporous cells in

7

terms of efficiency, planar perovskites are now almost as efficient as others.

Many perovskites are synthesized by using solid state reactions giving polycrystalline samples. The starting materials are the simple binary oxides or pure elements which are reacted at relatively high temperature involving the problems since certain starting oxides (e.g. PbO) may vaporize. The reaction temperature can be lowered by applying microwave synthesis techniques and thus minimizing the loss of volatile components. Powders and thin films with controlled levels of dopants have been prepared with the Sol-Gel technique using metal alkoxides as precursors. Thin films of ferroelectrics have been successfully prepared by physical vapor deposition (PVD) or pulsed laser deposition (PLD). [5] During recent years, several research groups have succeeded in growing single crystals of several families of perovskite related compounds from molten alkali carbonates or other fluxes such as hydroxides or halides.The perovskite film quality is very important and is therefore processed by either vacuum or solution methods.Initially, vacuum-deposited films gave the best devices, but this process requires the co-evaporation of the organic (methylammonium) component as well as the inorganic (lead halide) components at th same time .Further, necessitating specially designed evaporation chambers which are not available openly and commonly to all researchers. As a result, there have been significant efforts made in order to improve the solution-processed devices, as these are simpler and allow low-temperature processing .Typically, the active layer of a perovskite solar cell is deposited through either one or two-step process.

In the one-step process, a precursor solution is coated and then converted to the perovskite film upon heating. In the two-step process, the metal halide (such as PbI2) and organic components (such as CH3NH3I) are spin-coated in separate and subsequent films.

The main issues for practical device fabrication of perovskite solar cells are film quality and thickness. The light-harvesting (active) perovskite layer needs to be several nanometers thick with high uniformity which could be difficult. Unless the deposition conditions and temperatures are optimized which forms a rough surface with incomplete coverage. Therefore, thicker interface layers are used in order to make improvements to film quality which have been achieved through a variety of methods.[8]

Fig – 2.2.1 layers of perovskites

The rapid improvement of perovskite solar cells has made them the rising star of the photovoltaics world and of huge interest to the academic community because their operational methods are still relatively new and there is great opportunity for further research into the basic physics around perovskites. The hybrid organic-inorganic perovskite materials can be manufactured with simpler wet chemistry techniques in a traditional lab environment out of which methylammonium and formamidine lead trihalides also known as hybrid perovskites are most widely used and have been creating using a variety of solution deposition

8

techniques such as spin coating, slot-die coating, blade coating, spray coating, inkjet printing, screen printing, electrodeposition, and vapor deposition techniques. Perovskite solar cells based on organometal halides represent an emerging photovoltaic technology.

In 2009 a liquid-based dye-sensitized solar cell structure was first discovered due to the adsorption of methylammonium lead halide perovskite on a nanocrystalline TiO2 surface producing a photocurrent with a power conversion efficiency of around 3-4%. It was doubled after 2 years by the optimization of the perovskite coating conditions. However, the liquid-based perovskite solar cell receives little attention because of its stability issues, including the instant dissolution of the perovskite in a liquid electrolyte which therefore led to a long-term, stable and highly efficient ( 10%) perovskite solar cell which was was∼ developed further in 2012 by substituting the solid hole conductor with a liquid electrolyte. Efficiencies have quickly risen to 18% in just 2 years with the use of cheap organometal halide perovskite materials and perovskite solar cells which are a promising photovoltaic technology. [8]

A study of the formation and structure of forms of perovskites will help to develop many applications including solar cells. Perovskites share the same crystal structure as the natural perovskite mineral calcium titanite (CaTiO3). Substituting other elements or chemical groups in place of the calcium, titanium and oxygen creates unnatural hybrid perovskites. Adding organic layers can lead to nanostructures that enhance the stability of the overall material. The researchers later revealed how intermediate crystal fragments formed within a solvent mixture provide a scaffold that facilitates the crystallization of the desired RDPs. These are further generally used for making perovskites for other applications like light-emitting diodes, transistors, catalysts, sensors and highly selective gas storage materials. The most studied perovskites are oxides due to their electrical properties of ferroelectricity or superconductivity.

Halide perovskites received little attention until layered organometal halide perovskites were reported to exhibit a semiconductor-to-metal transition with increasing dimensionality. In addition to changes in electrical properties, the band gap decreased with increased dimensionality from 2D to 3D. A narrow band gap is beneficial for solar cell applications. At the given TiO2 film thickness of about 3.6 μm, CH3MH3PbI3 perovskite showed an absorption coefficient that was 10 times greater than that of the conventional ruthenium based molecular dye. Since organolead halide perovskite is an ionic crystal, it easily dissolves in a polar solvent. Thus, organolead halide perovskite is not suitable for the liquid electrolyte-based sensitized solar cells because of stability concerns. This instability problem was solved by substituting a solid hole conductor for the liquid electrolyte.

Deposition methods for fabrication in detail:

The solution-based processing method can be classified into one-step solution deposition and two-step solution deposition. In one-step deposition perovskite solution, which is prepared by mixing lead halide and organic halide together is directly deposited through various coating methods (such as spin coating, spraying, blade coating, and slot-die coating) in order to form perovskite film. One-step deposition is simple, fast, and inexpensive but the perovskite film uniformity and quality are needed to be controlled. In the two-step deposition, the lead halide film is first deposited then reacts with organic halide to form perovskite film. This reaction takes time to complete but it can be facilitated by adding Lewis-bases or partial organic halide into lead halide precursors. In two-step deposition method, the volume expansion during the conversion of lead halide to perovskite can lead to pinholes in order to realize a better film quality. The vapor phase deposition processes can be categorized into physical vapor deposition (PVD) and chemical vapor deposition (CVD). PVD refers to the evaporation of a perovskite or its precursor to form a thin perovskite film on the substrate, which is free of solvent. While CVD involves the reaction of organic halide vapor with the lead halide thin film to convert it into the perovskite film. A solution-based CVD, aerosol-assisted CVD (AACVD) was also introduced to fabricate halide perovskite films, such as CH3NH3PbI3, CH3NH3PbBr3,

9

and Cs2SnI6.

1. One-step solution deposition: - In one-step solution processing, a lead halide and a methylammonium halide can be dissolved in a solvent and spin coated onto a substrate. Subsequent evaporation and convective self-assembly during spinning results in dense layers of well crystallized perovskite materials due to the strong ionic interactions within the material. However, simple spin-coating does not yield homogenous layers, instead requires the addition of chemicals such as GBL, DMSO, toluene drips etc. Simple solution processing results in the presence of voids, platelets, and other defects in the layer, which may decrease the efficiency of a solar cell. Another technique using room temperature solvent-solvent extraction produces high-quality crystalline films with precise control over thickness down to 20 nanometers across areas several centimeters square without generating pinholes.

In this method "perovskite precursors are dissolved in a solvent called NMP and coated onto a substrate. Then, instead of heating, the substrate is bathed in diethyl ether, a second solvent that selectively grabs the NMP solvent and whisks it away. In another solution processed method, the mixture of lead iodide and methylammonium halide dissolved in DMF is preheated. Then the mixture is spin coated on a substrate maintained at higher temperature. This method produces uniform films of up to 1 mm grain size. Pb halide perovskites can be fabricated from either PbI2 precursor or non-PbI2 precursors, such as PbCl2, Pb (Ac)2, and Pb (SCN)2 giving films different properties. [7]

2. Two-step solution deposition: - In 2015, a new approach for the formation PbI2 nanostructure and the use of high CH3NH3I concentration have been adopted in order to form a high-quality perovskite film with better photovoltaic performances. On the other hand, a self-assembled porous PbI2 is formed by incorporating small amounts of additives into the PbI2 precursor solutions which facilitates the conversion of perovskite without any PbI2 residue. Moreover, by employing a relatively high CH3NH3I concentration and firmly crystallized and uniform CH3NH3PbI3 film is formed. [7]

10

03. Structure of perovskites

The structures of the perovskite-type compounds have been studied by many researchers. The exact nature

of the structure involved is still in doubt in many cases. Conflicting reports in the literature make the job of

assigning the correct structure and even symmetry difficult to any perovskite- type compound. The simplest

form of the perovskite structure is like a simple cubic cell with one ABX3 formula unit per unit cell. In this

case the A ions are at the corners of the unit cell and the B ion at the centre whereas the negative ions

occupies the face-centred positions.

Figure 3.1 shows the unit cell of CaTiO3

Figure 3.1 shows the unit cell of CaTiO3 as an example of the perovskite structure.A perfect cubic unit cell

is only present within SrTiO3.Generally, the unit cell of most perovskites is slightly distorted due to the

steric constraints caused by different combinations of ionic radii. The structure of perovskite is adopted by

many oxides which have the same chemical formula ABO3. The idealized form is a cubic structure is rarely

found but the orthorhombic and tetragonal forms are the mostly found non-cubic variants. Although the

perovskite structure is named after a non-idealized mineral form CaTiO3 mineral CaTiO3. SrTiO3 and

CaRbF3 are some examples of cubic perovskites. Barium titanite is an example of a perovskite which can

take on the rhombohedral, orthorhombic, tetragonal and cubic forms depending on temperature. IN the ideal

cubic unit cell , the type A atom sits at corner positions of the cube (0, 0, 0) and the type B atom sits at the

body-centre position (1/2, 1/2, 1/2) and oxygen atoms sit at face cantered positions (1/2, 1/2, 0), (1/2, 0, 1/2)

and (0, 1/2, 1/2).

There are three types of cation-pairings possible:

A2+B4+X2−3, 2:4 perovskites

A3+B3+X2−3, 3:3 perovskites

A+B5+X2−3, 1:5 perovskites.

The size of relative ion requires stability of the cubic structure to be quite stringent and slight buckling

because the distortion can produce several lower-symmetry distorted versions in which the coordination

11

numbers of A cations, B cations or both are reduced. Tilting of the BO6 octahedra reduces the coordination

of an undersized A cation from 12 to as low as 8. Conversely, off-centring of an undersized B cation within

its octahedron allows it to attain a stable bonding pattern. The resulting electric dipole is responsible for the

property of ferroelectricity and shown by perovskites such as BaTiO3 that distort in this fashion.[9]

Proton-conducting compounds with a perovskite structure are rare earths LaErO3 (Larring and Norby, 1994)

and LaScO3 (Fujii et al., 1998). In so-called complex perovskites, significant non-stoichiometries are used

in order to enhance the proton conductivity. A prominent example with a high cation non-stoichiometry is

Ba3Ca1.18Nb1.82O8.73 (BCN18) (Norby, 1999). Hydration of proton-conducting perovskites with high

oxygen deficiency allows for increased proton contents. Ba2InSnO5.5 and Ba2In2O5, for example, may

take up 0.5 protons (Schober, 1998) and one proton (Fischer et al., 1999) per unit cell, respectively. The first

HOIP-based PV device was reported by Kojima et al. in 2009, who used methylammonium lead iodide

(CH3NH3PbI3, MAPbI3) and methylammonium lead bromide (CH3NH3PbBr3, MAPbBr3) as the

sensitizers to fabricate dye-sensitized solar cells (DSSCs) with a liquid electrolyte. Because of a low power

conversation efficiencies (PCEs) of ~3% and poor device stability, HOIPs as light absorbing materials

received little attention. In 2012, the liquid electrolyte was replaced with a solid-state hole transport material

(HTM), and the PCE of MAPbI3-based solar cells increased to ~10%. These revolutionary findings opened

a new era of the emerging perovskite solar cells (PSCs) and spread the so-called “perovskite fever” all

around the world [14–16]. Thanks to the tremendous efforts in the past few years, PSCs have rapidly

progressed and reached 22.1% PCE. [10]

Fig. 3.2 shows some major milestones in the progress of PSCs,

It includes the device evolution from dye-sensitized to planar structure and the advancements in the solvent

and compositional engineering techniques. This successful progress also stimulated a great interest in this

emerging PV technology, as the annual number of articles published with the topic of PSCs has increased

from a single digit number in 2012 to ~2300 in 2016.

12

Fig 3.3- structure of cubic perovskite

A new method to fabricate high-performance inverted Perovskite Solar Cells by involving Phenethyl

ammonium bromide (PEABr) as passivator. During the process of fabrication PEABr diffuses into 3D

perovskite and form a mixed 3D/2D structure at the lower interface. This structure will restrain the charge

recombination and reduce the trap state density at the transport layer or the perovskite interface and bulk of

3D perovskite. Due to the bottom-up passivation effects, mixed 3D/2D PSCs achieve an improved PCE

from 17.59% to 19.46%, in combination with enhanced long-term air stability. This 3D/2D mix structure

demonstrates a great potential for developing high-performance and high stability PSCs.[9]This part traces

the remarkable evolution mainly from the perspectives of device architecture and material deposition

method by focusing on the early developments of the materials and notable devices with excellent

performance and technical advances in their methods of preparation and the future of the field.It has been

found by the researchers that from 2012 to 2016, the solar cells which are based on hybrid organic–inorganic

perovskites have emerged as a promising photovoltaic (PV) technology due to their high-power conversion

efficiencies and low-cost fabrication methods. The rapid evolution of this emerging PV technology from its

inclusion as an absorbing dye in dye-sensitized solar cells to stand alone devices (with efficiency >22%) has

made perovskite solar cells (PSCs) an exciting and important field of research.It has been found that the

major advancements of this rapid progress related to the evolution of device architecture, film deposition

method, device engineering techniques are critical factors which leads to the development of PSCs. In last

50 years many facts of science states that the Enormous utility is shown in the perovskite structure.

Beginning from its applications in high-temperature superconductors to piezoelectric sensors, the most

widely used application of perovskite structure is formation of array of cutting-edge areas in field of solid-

state physics and materials science. The combination of structural properties and unique charge carrier

dynamics of hybrid metal-halide perovskites are used to highlight why this class of materials is so promising

for low-cost, yet high-performance devices. [10]

13

14

04. Types of perovskites structures

Generally, there are different types of perovskite structures, but these are the most basic and most widely used forms of perovskite materials.

1. Simple Perovskites 2. Layered perovskites

Fig 4 – classification of perovskites

Let us first see the Layered perovskites

Layered perovskites consist of infinite 2D slabs having ABO3 type structure which are further separated by some motif. The general formula for the layers is: A(n-1) B(n)O(3n+1). In this formula, "n" indicates the size of the 2D slabs when n=1 means the slab is one BO6 octahedron thick. When n=2 means two BO6 octahedra thick. The clearest examples of this are the n=1 and n=2 Ruddleson-Popper phases Sr 2RuO4, and Sr3Ru2O7. For these phases, Sr is the A cation, and Ru is the B cation.The properties which help in characterizing the layered perovskites are:

1) the motif which separates the layers,

2) the offsetting of the layers from each other.

So here the separating motif is a layer of Sr2 and the perovskite slabs are offset by a (1/2,1/2) translation. It is possible, and perhaps appropriate to think of Ruddleson Popper phases as the general formula as A(n+1)BnO(3n+1) indicating that the outer A atoms as a part of the 2D perovskite slabs

or them as {A2}-{A(n1)BnO(3n+1)} because that relates them more consistently to the other layered perovskites. The n=2 phase Bi3TiNbO9 is representative of the Aurivillius phases which have the general formula

15

{Bi2O2}-{A(n-1)B2O7}where Ti and Nb are statistically dispersed on the B site. The formula can be re-written as: {Bi2O2}-Bi(Ti,Nb)2O7. The separating motif for all the Aurivillius phases is a rock-salt Bi2O2 layer. For example, Bi is also the A cation, but that needn't be the case. Again, the displacement of the perovskite slabs is a (1/2,1/2) translation. Perovskites may be structured in layers, with the ABO3 structure separated by thin sheets of intrusive material.

The different forms of intrusions based on the chemical properties of the intrusion are defined as [11]:

Aurivillius phase: the intruding layer is composed of a [Bi2O2]2+ ion, occurring every n ABO3 layer, leading to an overall chemical formula of [Bi2O2]-A(n−1) B2O7. Their oxide ion-conducting properties were first discovered in the 1970s by Takahashi et al., and they have been used for this purpose ever since.[12]

Dion−Jacobson phase: the intruding layer is composed of an alkali metal (M) every n ABO3 layer, giving the overall formula as M+A(n−1)BnO(3n+1)

Ruddlesden-Popper phase: the simplest of the phases, the intruding layer occurs between everyone

(n = 1) or two (n = 2) layers of the ABO3 lattice. Ruddlesden−Popper phases have a similar relationship to perovskites in terms of atomic radii of elements with A typically being large (such as La [13]or Sr[14]) with the B ion being much smaller typically a transition metal (such as Mn[15], or Co[16]).

Fig 4.1- layered perovskites

Types of layered perovskites are:-

(A) SrTiO3 - Cubic Perovskites:

The general formula for a perovskite is ABO3 where A and B are cations. The easiest way to visualize the structure is in terms of the BO6 octahedra which shares its corners infinitely in all 3 dimensions by making a very nice and symmetric structure. The A cations occupy every hole which is created by the 8 BO 6

octahedra's giving the A cation a 12-fold oxygen coordination and the B-cation a 6-fold oxygen coordination. For example, (SrTiO3) the Sr atoms sit in the 12 coordinate A site, while the Ti atoms occupy the 6 coordinate B site. There are many ABO3 compounds for which the ideal cubic structure is distorted to a lower symmetry (e.g. tetragonal, orthorhombic, etc.)

Fig 4.2 cubic perovskites

16

(B) Sr2FeMoO6 - Double Perovskites:

The double perovskite structure is named so because of the presence of unit cells twice as that in perovskites. It has the same architecture of 12 coordinate A sites and 6 coordinate B sites, but two cations are ordered on the B site. For example, Sr2FeMoO6 in this the Fe and Mo atoms have ordered in a 3D chessboard type fashion.

Fig 4.3- double layered perovskites

© CH3NH3PbX3 perovskite light absorber: structure

The perovskite structures having the general formula of ABX3

(X = oxygen, carbon, nitrogen or halogen)

A cation is occupied in a cubo-octahedral site

and B cation is occupied in an octahedral site.

When O2− anion is used, A and B are usually divalent and tetravalent, respectively. However, in order to fulfill charge neutrality perovskites containing halogen anions allow both the monovalent and divalent cations in A and B sites respectively. In CH3NH3PbI3, the A-site cation is CH3NH3+ and the B-site cation is Pb2+.

Fig 4.4- perovskite light absorber

17

Manipulation of layered perovskites

The manipulation of the orientation of crystal from the thermodynamic equilibrium states is desired in layered hybrid perovskite films to direct charge transport and enhance the perovskite devices performance. Here we report a templated growth mechanism of layered perovskites from 3D-like perovskites which can be a general design rule to align layered perovskites along the out-of-plane direction in films made by both spin-coating and scalable blading process. The method involves suppressing the nucleation of both layered and 3D perovskites inside the perovskite solution using additional ammonium halide salts, which forces the film formation starts from solution surface. The fast drying of solvent at liquid surface leaves 3D-like perovskites which surprisingly templates the growth of layered perovskites, enabled by the periodic corner-sharing octahedra networks on the surface of 3D-like perovskites. This discovery provides deep insights into the nucleation behavior of octahedra-array-based perovskite materials, representing a general strategy to manipulate the orientation of layered perovskites.

layered perovskites are highly electrically anisotropic, because the charge transport along out of plane (OP) direction is much hindered by the low-conducting organic spacing layers. Therefore, manipulating the orientation of layered perovskites becomes vital due to its significant impacts on the power conversion efficiency (PCE) of the resulted solar cells. Nevertheless, the orientation of layered perovskites might not be as desired, which is determined by both the thermodynamics of material structure as well as the kinetics in material formation process. Additionally, in-plane orientation (IP) orientation is common for two-dimensional (2D) materials with electron-rich structure due to the Van der Waals force or/and electrostatic induction between 2D materials and conductive substrates. For the butylamine (BA) based RP perovskites, the BA-terminated planes have the lowest surface energy, which lead to IP of this layered perovskite on many commonly used substrates to minimize the interface energy in the material system. On the other hand, OP orientation was reported to form in films made by some special formation processes, such as hot casting method1, despite that the OP orientation is rarely seen in RP perovskites with low layer number, such as n = 1. However, up to now, knowledge about manipulating the plane orientation of layered perovskites is still sparse. The driving force for the conditional OP orientation is unknown.

The blade coating process, which exhibits the merits of rapid film growth and less consumption of materials, has been regarded as a promising method for the fabrication of scalable perovskite films. However, achieving controllable film growth with a high quality is still a challenge. Herein, a rotating magnetic field (RMF) is proposed to manipulate the crystallization of perovskite thin films during blade coating in air. Improved film quality with good surface coverage and efficient charge transportation has been successfully accomplished in the as-produced smooth, uniform and dense perovskite layers. Thus, an enhanced photovoltaic performance with an average increase of 15% in power conversion efficiency was realized in∼ devices configured on the RMF-manipulated perovskite (CH3NH3PbI3) thin-film when compared with that of the conventional devices. This work well demonstrates a novel strategy to physically manipulate the crystallization of perovskite films with the purpose of a controllable and low-cost fabrication of high-performance PSCs.

18

Fig 4.5 - manipulation of perovskites

2D layered metal‐halide perovskites combine efficient exciton radiative recombination in crystal interior with long‐distance free‐carrier conduction at layer edges, which are promising candidates for realizing high‐performance photovoltaic, light‐emission and photodetection devices. The anisotropic electrical conductivity in layered perovskites imposes an additional requirement of orientational control for enabling favorable charge transport. However, rational fabrication of single‐crystalline nanostructures with pure crystallographic orientation is still elusive. Herein, large‐scale pure (101) ‐orientated 2D‐perovskite single‐crystalline nanowire arrays are realized by combining solvent engineering with the capillary‐bridge lithography technique. Ordered nucleation at liquid–air interface and unidirectional growth along the dewetting direction are demonstrated by fluorescence microscopy and grazing‐incidence X‐ray scattering in discrete capillary bridges. In consideration of crystal interior exhibiting high resistance arising from the serial insulating organic barriers and ultrafast dissociation of excitons to generate long‐lived free carriers at layer edges, ultrasensitive photodetectors are demonstrated with average responsivity exceeding 1.1 × 104 A W−1 and detectivity exceeding 9.1 × 1015 Jones.

19

05. Important features of perovskites Or

unique properties of perovskitesPerovskite materials exhibit many interesting and intriguing properties from both the theoretical and the application point of view. Colossal magnetoresistance, ferroelectricity, superconductivity, charge ordering, spin dependent transport, high thermopower and the interplay of structural, magnetic and transport properties are commonly observed features in this family. These compounds are used as sensors and catalyst electrodes in certain types of fuel cells and are candidates for memory devices and spintronics applications. Many superconducting ceramic materials (the high temperature superconductors) have perovskite-like structures, often with 3 or more metals including copper, and some oxygen positions left vacant. One prime example is yttrium barium copper oxide which can be insulating or superconducting depending on the oxygen content. Chemical engineers are considering a cobalt-based perovskite material as a replacement for platinum in catalytic converters in diesel vehicles. Physical properties of interest to materials science among perovskites include superconductivity, magnetoresistance, ionic conductivity, and a multitude of dielectric properties, which are of great importance in microelectronics and telecommunication. They are also some interests for scintillator as they have large light yield for radiation conversion. Because of the flexibility of bond angles inherent in the perovskite structure there are many different types of distortions which can occur from the ideal structure. These include tilting of the octahedra, displacements of the cations out of the centres of their coordination polyhedra, and distortions of the octahedra driven by electronic factors. Halide perovskites solar cells have the potential to exhibit higher energy conversion efficiencies with ultrathin films than conventional thin-film solar cells based on CdTe, CuInSe2 and Cu2 ZnSnSe4. The superior solar cell performance of halide perovskites could originate from its high optical absorption, comparable electron and hole effective mass, and electrically clean defect properties including point defects and grain boundaries. Perovskite materials exhibit many interesting properties due to its characteristic chemical nature such as the non-stoichiometry of the anions/cations, the valence mixture electronic structure, the distortion of the cation configuration etc

20

06. Properties of perovskitesPerovskite materials exhibit many interesting properties due to its characteristic chemical nature such as their non-stoichiometry of the anions and/or cations, the valence mixture electronic structure, the distortion of the cation configuration, and the mixed valence. Perovskites with transition metal ions on the B site show an enormous variety of magnetic properties. These show conductive nature and act as conducting oxides for e.g.; (LaSr)CoO3 .These also show magnetic behaviour and act as magnetic oxides for e.g.; (La,Ba)MnO3 .These act as non-linear optical oxides for e.g.,; KNbO3 .These act as super conducting oxides for e.g., (Ba,K)BiO3. Moreover, The possibility of Perovskites in synthesizing a multi component By partial substitution of cations in positions A and B Gives rise to various complex types with interesting properties such as; Dielectric properties, Optical properties, Ferroelectricity, Superconductivity, Piezoelectricity, Multiferroicity, Colossal magnetoresistance (CMR) and Catalytic activity etc .

1.Dielectric propertiesDielectric materials are the materials in which electro-static fields can persevere for a long time. It showed a great resistance to electric current channel below the action of the applied direct current voltage and diverge sharply in their simple electrical properties from conductive materials. Layers of these substances are generally inserted into capacitors to improve their performance, and the term dielectric refers to this application. Great dielectric permittivity or ferroelectric materials are of massive importance as electro ceramics for engineering and electronics industry. Ferroelectricity is generally described by a soft-mode model. Several routes have been pursued to explain the dielectric and mechanical properties starting from the simple structure BaTiO3 by the solid solution system Pb (Zr,Ti)O3 to other distinct families of materials. These routes care about the flexibility of chemical manipulation and submissiveness of the perovskites.

Relaxor ferroelectric is one of the routes, which show some effects because of the to slow reduction processes for temperatures above a glass transition such as big dielectric constants, a marked frequency dispersion and difference in dielectric constant.

General examples for relaxor ferroelectrics are lead lanthanum zirconate titanate (PZT) and lead magnesium niobite (PMN). Ferroelectrics can be considered as ferroelectric crystals and both of its high dielectric constant and low dielectric loss make perovskites one of the best candidates for tenable microwave device applications and dynamic random-access memory (DRAM).

2.Optical propertiesPerovskites have provided very special class of materials with excellent optical and photoluminescence properties. Studying the optical properties of single domain crystals of BaTiO3 at various temperatures showed that the refractive index of the crystal was nearly a constant value (2.4 from 20° to 90 °C & reached 2.46 at 120 °C). The single crystal of BaTiO3, 0.25 mm thick was found to transmit from 0.5 μ to 6 μ. The optical coefficient of strontium titanate single crystals were obtained from 0.20 μ to 17 μ in wavelength. The optical density of CaTiO3 showed absorption characteristics like those of SrTiO3 crystals with the exception that the absorptions are shifted to shorter wavelengths. Both compounds have been considered for high temperature infrared windows. SrTiO3 is considered as an excellent material for use with optically immersed infrared detectors.Some perovskites electro-optic coefficients of are nearly constant with temperature. Potassium tantalate niobate (KTN) is one of the perovskite oxides which has a large room temperature electro-optic effect and wide-angle fast optical beam scanner, therefore this type is not only useful to optical communications, but also to various other products that use optical beams, such as laser application. Using of perovskite laser host materials is a great deal. Luminescent properties of all uncommon earth ions in perovskite-type oxides are highly stable and can work in various environments in addition to they conceded to be the best candidate in field plasma display panel (PDP) devices and emission display (FED) because they are suitably conductive to release electric charges stored on the phosphor particle surfaces. Phosphors of rare earth ions doped perovskite type oxides could be widely used in displays, X-ray phosphors. One of the environment friendly photoluminescence (PL) is BaZrO3 which emits light in the visible region and prepared easily at low cost. The property of PL makes it promising for applications such as scintillators, solid state lightning, field emission displays, green photocatalyst and plasma displays.

3. FerroelectricityFerro electricity is the characteristic of certain material which have a certain spontaneous electric polarisation that can be reversed by the application of external electric field. Ferroelectricity is the phenomenon that occurs when an external electric field is applied to some materials leading to a spontaneous electric polarization. The discovery of ferroelectricity in perovskite-based materials and other barium titanate (BaTiO3) opened a new different application for ferroelectric materials, leading to significant interest in other types of ferroelectrics. The ferroelectric materials have dielectric constant twice larger in magnitude than those in ordinary dielectric. BaTiO3 is a well-known ferroelectric material with relative dielectric constant, its crystal at room temperature, exhibits no net polarization, in the absence of an external field, even though the dipoles of adjacent unit cells are aligned. Ferroelectric property is used to several purposes such as; in ultrasound imaging devices, fire sensors, infrared cameras, vibration sensors, tenable capacitors, memory devices, RAM and RFID cards, input devices in ultrasound imaging, and a. make sensors, capacitors, memory devices, etc.

4. SuperconductivitySuper conductivity is a set of physical properties obtained in the materials where the electrical resistance vanishes, and the magnetic flux is expelled. These types of materials are called super conductors. Certain materials once cooled under a specific serious temperature exhibited zero electrical resistance and expulsion of magnetic flux fields this phenomenon is called Superconductivity. The oxide perovskites structure type provides an excellent structural framework due to the existence of superconductivity. Perovskites which have Cu act as high-temperature superconductors. The first reported example of superconducting perovskites is La-Ba-Cu-O perovskite and there are many more. Perovskite oxides now eclipsed the use of Intermetallic compounds as source of many superconducting materials such as caesium tungsten bronzes and Sodium, potassium, rubidium. Type 2 group Superconducting “perovskites” metal-oxide ceramics are those compounds

21

which have specific ratio of 2 metal atoms to every 3 oxygen atoms. This type of superconductors is contained of alloys and metallic compounds (excluding for niobium, vanadium, and technetium), recently they achieve higher transition temperature than Type 1 superconductors.

5. PiezoelectricitySome materials have the capacity to produce an electric charge in reaction to applied mechanical stress is known as Piezoelectricity. Therefore, if definite crystals were subjected to mechanical strain, they became polarized at a degree which is proportional to the applied strain. On the other hand, they have some changed when they were exposed to an electric field which is known as the inverse piezoelectric effect. There is a difference between piezoelectric and ferroelectric materials, in the fires materials it requires some external impetus while in the second there is spontaneous alignment of electric dipoles by their mutual interaction. Therefore, all piezoelectric are not ferroelectric but all ferroelectrics are piezoelectric. Some synthetic piezoelectric materials are the piezoelectric ceramics with the perovskite crystal structure having a general formula of A2+B4+O2−3. Also, there are naturally occurring piezoelectric materials; quartz, cane sugar, collagen, topaz, Rochelle salt, tendon, etc.Perovskites materials Piezoelectricity property have many valuable scientific application such as; Cigarette lighter, Sensors, Microphones, High voltage and power source, Pick-ups, Pressure sensor, Force sensor, Strain gauge, Actuators, Piezoelectric motors, Piezoelectric motors, Nano-positioning in AFM, STM, Acuosto-optic modulators, Loudspeaker, Valves, Energy harvesting, AC voltage multiplier.

6. MultiferroicityMultiferroics include special class of materials showing concurrent ferroelectric, ferromagnetic, and ferro elastic ordering. The specialty of these materials localized in their ability to simultaneous utilization of both their magnetization and polarization states, a potential which make them excellent candidates for memory devices and sensors. Many multiferroics are transition metal oxides with perovskite crystal structure and include rare-earth manganite and ferrites. These materials show multiferroicity even at room temperature. Bismuth ferrite, a rhombohedral distorted perovskite (compounds with multiferroics property) possesses both anti-ferromagnetic and ferroelectric order for a widespread temperature range which is greatly above room temperature.Most of the ferromagnetic materials are generally metals and they must be an insulator because the absence of insulators limits the simultaneous occurrence of ferromagnetic and ferroelectric ordering The important requirement for ferroelectricity is a structural distortion from the high symmetry phase that removes the centre of inversion and allows an electric polarization . It has been found that even in the absence of any structural distortion, magnetic spin ordering can produce ferroelectricity.

Fig.6 Conditions required for ferroelectricity (polarization) and ferromagnetism (unpaired electron spin motion). Multiferroics have great technological potential importance due to the co-occurrence of magnetic order and ferroelectric polarization joint in a single-phase material. Multiferroic materials open promising opportunities for spintronics devices and designing novel microelectronic. It has been found that even in the absence of any structural distortion, magnetic spin ordering can produce ferroelectricity. Multiferroicity, a co-occurrence of natural ferroelectric and ferromagnetic moments, is an uncommon phenomenon due to the minor number of asymmetry magnetic point groups that permit an unplanned polarization. Multiferroic materials classified into Type I & type II Multiferroic. Type I includes the structures with nonpolar-to-polar phase transition which responsible about the breaking of reversal equilibrium leading to ferroelectricity at high temperatures. While in type II the primary order parameter is the staggered (antiferromagnetic) magnetization. In addition, if the magnetic ordering goes below a given temperature, it lowers both magneto-structural coupling to the crystal structure (this gives rise to an electrically polar state) and the symmetry group from polar magnetic phase to a nonpolar parent phase making wrong ferroelectricity therefore ferroelectric order and magnetic factors are closely joined .

7. Colossal magneto resistance (CMR)Colossal magneto resistance (CMR) is a property of materials (mostly manganese-based perovskite oxides) that allows them to change their electrical resistance in the presence of a magnetic field. The discovery of this property (CMR) affect the divalent alkaline-earth ion doped perovskite manganite RE1−xAExMnO3, where AE represents divalent alkaline earth ions (Ca, Sr, Ba) and RE is trivalent rare-earth (La, Pr, Sm, etc.)Magnetic phases are observed depending on the orbital occupancy of the manganese ions and the associated orbital order, different. In these compounds, ordering temperatures of similar magnitude for both degrees of freedom because their orbitals and spins are strongly coupled.

On the other hand, magnetic frustration, low dimensionality, and quantum effects lead to very peculiar phase graphs with or without magnetic long-range order. In unfulfilled lattices the degeneracy of the magnetic zero state can be frequently lifted by second order energy scale or quantum fluctuations. Generally, CMR effect is closely related to its manganites which are correlated electron systems with interplay among the lattice spin, Jahn-Taller effect, charge & orbital degrees of freedom, electronic phase separation, charge ordering, etc.

22

8. Catalytic activityPerovskites displayed exceptional catalytic action and great chemical stability therefor it includes in the catalysis of changed reactions. Also, it can be defined as an oxidation or oxygen-activated catalyst and as a model of active sites. The perovskite structure showed high catalytic activity in addition their stability allowed the preparation of several compounds from elements with uncommon valence statuses or a great extent of oxygen lack. They also can act as motor exhaust gas catalyst, cleaning catalyst, and intelligent automobile catalyst for various catalytic environmental reactions. Some Perovskite types (containing Cu, Co, Mn, or Fe) showed catalytic action to the straight decay of NO at high temperature due to the occurrence of oxygen deficiency and the simple removal of the surface oxygen in the a shape of a reaction product. Perovskite revealed a great effect as a vehicle catalyst, intelligent catalyst, removal of CO &NO, effective catalyst and Not combusted hydrocarbons. It can show redox properties to reserve unlimited scattering state and when oxidation occurs fine metal bits of Pd will formed with radius of 1–3 nm. This led to partial replacement of Pd into and sedimentation from the structure of the perovskite under decreasing and oxidizing states showing a great scattering state of Pd. This cycle improved the long-standing reliability of Pd through the pollutant's elimination from the exhaust gas. The great stability of

the perovskite structure and the unlimited spreading state of Pd were the cause of calling it as intelligent catalyst (see Table).

Table- Some properties of perovskite oxides.Typical property Typical compoundFerromagnetic BaTiO3, PdTiO3

Piezoelectricity Pb(Zr, Ti)O3, (Bi, Na)TiO3

Electrical conductivity ReO3, SrFeO3, LaCrO3, LaCoO3, LaNiO3

Superconductivity La0.9Sr0.1CuO3, YBa2Cu3O7, HgBa2Ca2Cu2O8

Ion conductivity La(Ca)AlO3 BaZrO3, CaTiO3, SrZrO3, BaCeO3, La(Sr)Ga(Mg)O3,

Magnetic property LaMnO3, LaFeO3, La2NiMnO6

Catalytic property LaCoO3, LaMnO3, BaCuO3

Electrode La0.6Sr0.4CoO3, La0.8Ca0.2MnO3

23

07. Applications of perovskites

Perovskites have wide applications due to its stable structure, large number of compounds, variety of properties. Inorganic perovskite type oxides are attractive nanomaterial for varied applications due to its large number of compounds, very stable structure, variety of properties and several practical applications. Some of these compounds' nanomaterial are wildly applied in catalysis of many chemical engendering fields. The activity of these oxides as catalyst is better than any other transition metals and precious metal oxides. Depending on Perovskite oxides distinct variety of properties they became useful for various applications such as; Thin film capacitors, Non-volatile memories, Photo-electrochemical cells, Recording applications, Read heads in hard disks, Spintronics devices, Laser applications, For windows to protect from high temperature infrared radiations, High temperature heating applications, Thermal barrier coatings, Frequency filters for wireless communications, Non-volatile memories, Sensors, actuators and transducers, Drug delivery, Catalysts in modern chemical industry, Ultra-sonic imaging, ultrasonic & underwater devices. Perovskites being efficient and economical are majorly used in LEDs, LASER, photo electrolysis, perovskite solar cells etc. Some more important applications of different perovskite structured are listed in Table below

Table 7. Some important applications perovskite structured and their properties.

Reference compound Properties Existing and potential applications NotesBaTiO3 Ferroelectricity, high dielectric constant,

piezoelectricityMultilayer ceramic capacitors (MLCCs), embedded capacitance, PTCR resistors,

Most widely used dielectric ceramicTC = 125 °C

(Ba,Sr)TiO3 Non-linear dielectric properties Tuneable microwave devices Used in the paraelectric state

Pb(Zr,Ti)O3 Piezoelectricity, Ferroelectricity Piezoelectric transducers and actuators, ferroelectric memories (FERAMs) PZT: most successful piezoelectric material

Bi4Ti3O12 Ferroelectric with high Curie temperature High-temperature actuators, FeRAMs Aurivillius compoundTC = 675 °C

(K0.5Na0.5)NbO3, Na0.5Bi0.5TiO3 Ferroelectricity, piezoelectricity Lead-free piezoceramics Performances not yet comparable to PZT but rapid progress

(Pb,La)(Ti,Zr)O3 Transparent ferroelectric Optoelectronic devices First transparent ferroelectric ceramic

BiFeO3 Magnetoelectric coupling, high Curie temperature Magnetic field detectors, memories Most investigated multiferroic compound.

TC = 850 °C

PbMg1/3Nb2/3O3 Relaxor ferroelectric Capacitors, actuators frequency-dependent properties, High permittivity, large electro strictive coefficients,

SrRuO3 Ferromagnetism Electrode material for epitaxial ferroelectric thin films

(La, A)MnO3A = Ca, Sr, Ba

Ferromagnetism, spin-polarized electrons, giant magnetoresistance Magnetic field sensors, spin electronic devices

SrTiO3Incipient ferroelectricity, thermoelectric power, metallic electronic conduction when n-doped, mixed conduction when p-doped, photocatalyst

Alternative gate dielectric material, barrier layer capacitors, photo assisted water splitting, substrate for epitaxial growth,

Multifunctional material

LaGaO3BaIn2O5 Oxide-ion conduction Electrolyte in solid oxide fuel cells (SOFCs) BaIn2O5 is an oxygen deficient perovskite with

brownmillerite structure.

BaCeO3, BaZrO3 Proton conduction Electrolyte in protonic solid oxide fuel cells (P-SOFCs) High protonic conduction at 500–700 °C

(La,Sr)BO3(B = Mn, Fe, Co) Mixed conduction, catalyst

controlled oxidation of hydrocarbons, Cathode material in SOFCs, membrane reactors, oxygen separation membranes,

Used for SOFC cathodes

LaAlO3YAlO3 Host materials for rare-earth luminescent ions, Substrates for epitaxial film deposition, Lasers

Recently, they utilized in electrochemical sensing of alcohols, acetone, glucose, gases, amino acids, H2O2, sensitivity, excellent reproducibility, unique long-term stability, anti-interference ability and neurotransmitters exhibiting good selectivity, etc. In addition, some perovskites are worthy applicants for the development of effective anodic catalysts for direct fuel cells viewing high catalytic performance. Some details of the application are summarized in the following.

24

(A.) Perovskite Solar Cell SOLAR CELL is a device which converts light energy to electrical energy using any photochemical reaction or effect. To begin a new era for the utilisation of solar power from polycrystalline silicon solar cells. We have shifted to perovskite solar cells because of their easy availability and usage. Before, moving on to

perovskite solar cells let us see some disadvantages of using silicon solar cell.

Silicon solar panels are vulnerable to temperature fluctuations. They have become ineffective in the areas which have low temperature and experience show fall. An ideal warm weather is necessary to increase the temperature of solar panels But a great increase can be problematic in future. Rising temperature can blow off the performance level of the system. The silicon solar cell's polluted ambience can hamper the performance of the panels. The basic shape of these silicon solar cells is cylindrical with rounded edges. And the characteristic shape accounts its functional effectiveness. But, the structural feature leads to wastage of original silicon. TRADITIONAL SILICON CELLS REQUIRE EXPENSIVE MULTI-STEP PROCESSES TO BE CONDUCTED AT HIGH TEMPERATURES

(>1000 °C) UNDER HIGH VACUUM CONDITIONS IN SPECIAL CLEANROOM. MEANWHILE, THE HYBRID ORGANIC-INORGANIC PEROVSKITE MATERIAL CAN BE MANUFACTURED WITH SIMPLER WET

CHEMISTRY TECHNIQUES IN A TRADITIONAL LAB ENVIRONMENT. MOST OF THE HYBRID PEROVSKITES, HAVE BEEN CREATED USING A VARIETY OF SOLUTION DEPOSITION TECHNIQUES, SUCH AS SPIN COATING, SLOT-DIE COATING, BLADE COATING, SPRAY COATING, INKJET PRINTING, SCREEN PRINTING, ELECTRODEPOSITION, AND VAPOR DEPOSITION TECHNIQUES.

Due to these disadvantages we shifted onto perovskite solar cells which are moreover cheaper than all others. So, we can say that perovskite solar cell is a type of solar cell which includes a perovskite absorber which act as the light-harvesting active layer which produces electricity from sunlight. Perovskite absorber materials are extremely cheap to produce and simple to manufacture. Perovskite solar cells hold an advantage over traditional silicon solar cells in the simplicity of their processing and their tolerance to internal defects. Perovskites enables researchers to produce high quality, fully functional solar cells that can be used as a reliable baseline. At the most basic level, most perovskite-based solar cells are based upon a transparent conductive oxide coated glass substrate with evaporated metal cathode and top encapsulation. As such, our existing substrate infrastructure and perovskite materials are already being used in high-performance solution-processed perovskite devices.Metal halide perovskites possess unique features that make them useful for solar cell applications: -

The raw materials used, and the possible fabrication methods are both low costs. Their high absorption coefficient enables ultrathin films of around 500 nm to absorb the complete visible solar spectrum.

Traditional silicon solar cell processing is quite expensive, a multistep process which requires high temperature and vacuum facilities in special clean rooms to produce high purity silicon wafers whereas, and perovskite solar cell processing is simple and cost effective.

Fig 7.1 - processing of perovskite solar cell

In this process technique the deposition of CH3NH3PbI3 perovskite on a mesoporous Tio2 substrate takes place in two methods that is, one step and two step coating methods. In one step coating method CH3NH3I and PbI2 are dissolved in appropriate protic solvent gamma-butyrolactone (GBL) or dimethyl sulfoxide (DMSO) and this applied as coating solution, the processes like drying and annealing are followed by spin coated methods. In two step coating method to the TiO2 substrate PbI2 solution is coated first to form PbI2 film and then 2-proponol solution of CH3NH3I is added to spinning PbI2 film. In order to get high quality perovskite film, it is important to adjust coating parameters like temperature, time, spinning rate, viscosity, solution wettability etc .Combination of both these features result in the possibility to create low cost, high efficiency, thin, lightweight and flexible solar modules. Depending upon the role of Perovskite material in the device and the nature of the electrodes used (top and bottom) Perovskite solar cells architecture will be decided. Basically, perovskite is a light absorbing layer, usually perovskite is built around dye sensitized solar cell (DSSC) architecture. Positive charges are extracted by the transparent bottom electrode (cathode), which is predominantly be divided into 'sensitized' and charge transport occurs in thin-film, majority hole or electron transport occurs in the bulk of the perovskite itself. Like the sensitization in dye-sensitized solar cells, the perovskite material is coated onto a charge-conducting mesoporous scaffold-most commonly TiO2 – as light absorber. The generated electrons are transferred from the perovskite layer to the mesoporous TiO2 sensitized layer through which they are transported to the electrode and extracted into the external circuit. A perovskite solar cell (PSC) is a type of solar cell which includes a perovskite structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer. Perovskite materials, such as methylammonium lead halides and all-inorganic cesium lead halide, are cheap to produce and simple to manufacture. Perovskite was first used as a sensitizer in dye-sensitized solid-state devices in which molecular dye was replaced by perovskite. In the sensitization concept, HTM should be fully infiltrated inside the mesoporous oxide layer to induce heterojunction. In addition, oxide layers with electron accepting properties are required to separate the photo-excited electrons in perovskite. Using this sensitization concept, a CH3NH3PbI3 nanodot-adsorbed 0.6 μm-thick TiO2 film demonstrated PCE of 9.7%, photocurrent density (Jsc) of 17.6 mA/cm2, and open-circuit voltage (Voc) of 888 mV.To understand the charge separation in this sensitized structure, a femtosecond transient absorption spectroscopic study was performed with TiO2 and Al2O3. No significant spectral differences between TiO2 and Al2O3 were observed, suggesting that perovskite solar cells may work even without an electron injecting layer.

25

FIG 7.2- EVOLUSTION OF PEROVSKITES

Structural evolution of perovskite solar cells:

(a) sensitization concept with surface adsorption of nanodot perovskite,

(b) meso-superstructure concept with non-injecting scaffold layer,

(c) pillared structure with a Nano oxide building block,

(d) planar pin heterojunction concept and the Spheres represent TiO2 in (a) and (c) and Al2O3 in (b).

Perovskite solar cells were confirmed to work in the absence of a mesoporous TiO2 layer. The CH3NH3PbI3−xClx thin layer coated Al2O3 film had a PCE of 10.9%. The Al2O3 served as a scaffold layer because electron injection from perovskite to Al2O3 was not allowed. This result implies that the sensitization concept is not always required for perovskite solar cell design. Moreover, this result suggests that electron transfer can occur in the perovskite layer. A pillared structure was proposed in which the pores of a mesoporous TiO2 film (pillars) were filled with perovskite instead of a surface coating.

FIG 7.3- PROCESSING POF DIFFERENT MATERIALS

A thin capping layer (over layer) was formed after infiltration with the perovskite. With this method, PCE of 12% was reported using CH3NH3PbI3 and polytriarylamine (PTAA). A higher PCE of 15% was achieved from the pillared structure with a two-step coating procedure. In this method, the CH3NH3PbI3 layer was prepared by dipping the PbI2 layer formed in mesoporous TiO2 film into a diluted CH3NH3I solution while the perovskite layer was in contact with spiroMeOTAD . Since an electron accepting oxide layer is not required, perovskite solar cells can be fabricated from junctions among the perovskite film (intrinsic layer), n-type thin TiO2 film, and p-type HTM film. The planar pin junction concept, in which 300 nm-thick CH3NH3PbI3−xClx film was prepared by co-evaporation of CH3NH3I and PbCl2, was confirmed to exhibit PCE over 15%. cross-sectional view of the planar structure in which the

deposited .CH3NH3PbI3−xClx film shows only (h k 0) peaks in the X-ray diffraction pattern, indicating that Cl− ions are placed in the axial position. One of the green sources of energy is solar energy because it can be used in replace of the fossil fuels energy. Solar radiation can be transformed to electrical energy in a suitable way building numerous uses for solar energy. It can be perfectly changed into electricity using photovoltaic solar cells which built on silicon. The disadvantage of silicon built solar cell is its high price of electricity produced from it, so develop solar cell with low cost is needed. Solar cells created on organic/ inorganic solid-state methyl ammonium lead halide hybrid perovskite are in used because it presented better points such 20% lower cost than that of traditional silicon solar cells in addition to the availability of the raw materials. Perovskite showed outstanding essential properties for photovoltaic applications like suitable band gap, excellent stability, long hole-electron diffusion length, high absorption coefficient, high carrier mobility & transport, low temperature of processing, charge carriers with small effective mass and easy processing steps. Perovskite material offers direct optical band gap of around 1. 5eV.Perovskite material offers long diffusion length and long minority carrier lifetimes. It has broad absorption range from visible to near infrared spectrum (800 nm) and high absorption coefficient (105 cm –1 cm). Perovskite cells deliver efficiencies of more than 22 percent. Perovskite material such as methylammonium lead halides are far inexpensive and simple to manufacture. It has high dielectric constant, fast charge separation process, long transport distance of electrons and holes and long carrier separation lifetime. This low-cost material helps in converting windows of buildings, top of cars and walls to achieve solar power generation. Perovskite uses less material in order to absorb same amount of light compare to silicon. Hence it is cheaper than silicon.

(B) Gas sensorsThere are a sum of necessities that the resources used as gas devices must content such as hydrothermal constancy, good similarity with the target gases, suitable electronic structure, resistance to poisoning, and alteration with existing skills. Perovskite oxides used as gas sensors like semiconductors, LaFeO3 and SrTiO3. They are interesting materials as gas sensors for their ideal band gap, thermal stability, and size difference between the cations of B-- and A sites. Perovskites materials which contain cobaltite, titanites, and ferrites were applied as gas sensors for spotting CO, NO2, methanol, ethanol, and hydrocarbons

(C) Glucose sensorIt is important to determined H2O2 and glucose in numerous fields in our live such as in food, pharmaceutical products and clinic. H2O2 is oxidizing agents in many neutrinos and industries. Glucose also is the basic metabolite in many of the living organisms and in clinical check of diabetes mellitus, and universal healthiness problem. Therefore, it is important to have excellent sensitive biosensors for determination both H2O2 and glucose. Although there are different types of enzymatic work as glucose sensors, but this enzyme lacks the stability due to its basic nature in addition its action was greatly affected by poisonous chemicals, temperature, humidity, etc. consequence, there must be searching for stable, sensitive, simple, and selective non-enzymatic glucose sensor such as inorganic

26

perovskite oxides. This sensor has perfect electrocatalytic activity toward glucose and H2O2 oxidation in alkaline medium due to the occurrence of huge number of active sites in the modifier.

(D) Neurotransmitters sensorIn the mammalian central nervous system, dopamine (DA) is an essential catecholamine neurotransmitter. The deficiency of this transmitter lead to Parkinson’s disease; therefore, its detection is very important but there is very big problem in detection of DA which is the interference of ascorbic acid (AA) and uric acid (UA) with its detection. Therefore, it is very important to find sensitively and selectively detector to DA even in presence of high concentration of AA and UA. After electrode modified of SrPdO3 (CpE/SrPdO3) it became very good electrochemical DA sensor in living liquids with exclusive long-term constancy and low discovery limit even in the occurrence of high level of AA and UA, it also can sense DA in human urine samples with full selectivity recovery, precision, accuracy, and detection limit .

(E) Solid oxide fuel cellsFuel cells are used as substitutes to ignition engines due to their possibility to reduce of the environmental pollution. They use specific type of chemical compound as energy source which transfer to electrical energy like battery. Fuel cells are more acceptable for use due to their effectiveness, spread nature, zero noise pollution, low emissions and its use in future hydrogen fuel economy. There are numerous categories of fuel cells, but solid oxide fuel cell are the greatest common samples of fuel cells. Due to the variances of electrically conductive characteristics of perovskites, they are selected as an active component in SOFC because they exhibited its properties of electrical conductivity which is comparable to that of metals with high ionic conductivity, and perfect mixed ionic and electronic conductivity .

(F) CatalystPerovskite oxides used universally as catalyst in new chemical manufacturing, showing suitable solid-state, surface, and morphological properties. Several perovskites oxides proved to have excellent catalytic activity to different reactions like hydrogen evolution, reduction reactions, and oxygen evolution.

(G) LASERA laser is a device which is built on the principles of quantum mechanics to create a beam of light where all the photons are in a coherent state — usually with the

same frequency and phase.IN 2014 researchers demonstrated that perovskites could generate laser light. Although perovskite light‐emitting devices are yet to

become industrially relevant. But, in merely two years, these devices have achieved those brightness's and efficiencies which the organic light‐emitting diodes

accomplished in two decades. Further advances say that these enable the formation of lower‐dimensionality layered and three‐dimensional perovskites,

nanostructures, charge‐transport materials, and device processing with architectural innovations. Low‐cost solution processed perovskite lasers have emerged as a

new application area in recent years.

FIG 7.4 - LASER

27

Methyl ammonium lead iodide perovskite (CH3NH3PbI3-xClx) cells were fashioned into optically pumped vertical – cavity surface – emitting lasers (VCSELs)

Which converted visible pumped light to near –IR laser light with an efficiency of 70%. . Physicochemical attributes like long ranged ambipolar charge transport,

long carrier lifetimes, photoluminescence QYs of nearly 40% for perovskite nanoparticles and 90% in bulk films, with large‐scale, defect‐free, easy solution

processing highlight their potential for laser materials. The size‐dependent colour variation property arising from “particle in a box,” quantum phenomena in

semiconductor materials, allows them to behave as low threshold light emitters like multi-coloured laser systems. In comparison with crystalline materials grown

in high temperatures like ZnSe or most organic semiconductors, two fundamental features are exclusive to perovskites, making them more promising as laser

materials. They are: 1) amplified stimulated emission (ASE), lower by one order of magnitude w.r.t. organic materials with long electron–hole recombination

times which is why they act as good gain medium in lasers, and 2) the perovskite emission colour can be broadly tuned over a large wavelength scale (350–700

nm) by controlled composition variation or morphology tuning. It is important to consider that lower dimensional perovskite materials, primarily nanoplatelets,

dots, disks, wires etc., achieved by morphology tailoring are highly desirable for controlled lasing because of their optical cavities.

Considerable research has been conducted to engineer these cavities for optical amplifications using primarily: 1) Fabry–Pérot (FP) cavity resonators, usually

forming at perovskite facets, 2) whispering gallery modes (WGM) which are trapped in cavities and multidirectional lasing happens due to total internal reflection,

and 3) Random lasing (RL) offered by various grain boundaries. In addition, other approaches like directional distributed grating and perovskite structures for

polaritonic lasing have been taken. In the following section, we provide specific examples catering to the above types. Finally, we briefly discuss the challenges

and goals to advance perovskite lasers. The Fabry–Pérot cavity resonator is the mostly used architecture, utilized in perovskite laser designs. Here, the optical

amplification via the FP cavity occurs between two reflective surfaces, like mirrors, photonic crystals, or the polished endings of nanowires. FP cavities stand out

because the lasing output frequency can be altered by deliberately tuning the cavity length. In addition, spectral purity, uni‐directional lasing, and high Q factors

with low ASE threshold leading to slower non‐radiative paths makes FP cavities ideal. In 2014, Deshler et al. 39 introduced methyl ammonium halide FP laser

systems by forming a cavity, shielding a MAPbX3 film between highly reflective Au and a dielectric surface. High (~70%) photoluminescent QYs observable at

significantly high pumping power (>100 Mw cm 2) establish that non‐radiative recombination paths are scarce, resulting in a high performing laser device. In

addition to real mirrors, as used by Deshler et al. as described above, photonic crystal and nanowire facets have been used as FP‐reflective surfaces. For example,

Chen et al .40 reported an FP perovskite micro‐laser by sandwiching MAPbI3 between two reflective facets of a photonic crystal. This architecture stands out due

to crystal purity and improved gain and is a step forward toward practical application. CH3NH3PbX3 nanowire‐based FP lasers have been realized by Yu et al .,41

which can emit light below diffraction limits. In this architecture, the ends of the perovskite halide nanowires act as FP resonators and encapsulate magnesium

fluoride (MgF2). The optical polarization in the nanowire active layer is along the wire‐axis, and the device operates at temperatures up to ~44 °C.

28

08. ADVANTAGES AND DISADVANTAGES OF USING PEROVSKITES

Perovskite is cheaper to produce than silicon and is also very efficient in absorbing light. Recent study has found the mineral also emits light. It uses less material compared to silicon to absorb same amount of light which results in cheaper solar power. Perovskites have been widely used in the fields of optics, photovoltaics, electronics, magnetics, catalysis, sensing, etc.

Now Imagine instead of buying and installing solar panels, solar cells could be sprayed on any surface like walls, windows, cars, backpacks etc. to generate energy. This(perovskite) material has demonstrated high absorption coefficient and can be produced on a large scale with no observed degradation over one year. The process of manufacturing a perovskite solar cell is also less complex than that of traditional silicon solar cells. It is also a low-cost solar technology and could further revolutionize the global solar industry.

On the disadvantages side, the technology is still in a very nascent stage and industry is sceptical using it to replace the traditional silicon PV technology. Degradation and stability are other concerns. However, some inherent shortcomings, such as low efficiency, power conversion efficiency, external quantum efficiency and poor stability limit their practical applications. Perovskite breaks down quickly when exposed to heat, snow, moisture etc. The material is toxic though the toxin level has gone down in recent years. Toxic materials are used in perovskites and their Commercialization process is just at beginning. These are also not stable enough and cannot last long. The technology looks promising and few firms have also promised to launch thin-film perovskite solar cell commercially by the end of 2018. Perovskite was chosen as one of the top 10 emerging technologies of 2016 by the World Economic Forum.

Though perovskite solar panels are not yet commercially viable, it is surely an emerging technology which firms are seriously considering. The research around the subject started way back in 2006 and in just a little over a decade the material has witnessed huge efficiency gains (more than 20%), which silicon cells took ages to achieve. The biggest issue in the field of perovskites currently is long-term instability which is due to degradation pathways involving external factors, such as water, light, and oxygen, and also as a result of intrinsic instability, such as degradation upon heating, because of the properties of the material. Several strategies have been proposed in order to improve stability, most successfully by changing component choice. Using mixed-cation systems (by including inorganic cations such as rubidium or cesium) has been shown to improve both stability and efficiency.

The first perovskite cells to exceed 20% efficiency used a mixed organic cation system, and many of the highest-efficiency systems published recently use inorganic components. Movement towards hydrophobic, UV-stable interfacial layers has also improved stability – for example by replacing TiO 2, which is susceptible to UV degradation, with SnO2.Stability has also been improved through use of surface passivation and by combining 2D-layered (Riddlesden-Popper) perovskites (which show better intrinsic stability, but poorer performance) with conventional 3D perovskites. These efforts (along with factors such as better encapsulation) have vastly improved the stability of perovskites since their initial introduction, and lifetimes are well on their way to meeting industrial standards – with recent work showing cells able to withstand a 1000-hour damp heat test. For a more in-depth discussion of methods to improve the perovskite stability, see Ocilla's guide.

Another issue which is needed to be fully sorted is the use of lead in perovskite compounds though it is used in much smaller quantities because the presence of lead in products for commercial use is problematic. Concerns remain about exposure to toxic lead compounds; some studies have suggested large-scale implementation of perovskites would require complete containment of degradation products. There is also potential for a lead alternative to be used in perovskite solar cells (such as tin-based perovskites). But the power conversion efficiency of such devices is still significantly behind lead-based devices, with the record for a tin-based perovskite currently standing at 9.0%. Some studies have also concluded that tin may have a higher environmental toxicity than lead, and other fewer toxic alternatives are required.

However, some inherent shortcomings, such as low efficiency, power conversion efficiency, external quantum efficiency and poor stability limit their practical applications. Perovskite breaks down quickly when exposed to heat, snow, moisture etc. The material is toxic though the toxin level has gone down in recent years. Toxic materials are used in perovskites and their Commercialization process is just at beginning. These are also not stable enough and cannot last long. Another major issue in terms of performance is the current-voltage hysteresis commonly seen in devices. The factors impacting hysteresis are still under debate, but it is most attributed to mobile ion migration in combination with high levels of recombination. Methods to reduce hysteresis include varying cell architecture, surface passivation, and increasing lead iodide content, as well as general strategies to reduce recombination.

To enable a truly low cost-per-watt, perovskite solar cells need to have achieved the much-heralded trio of high efficiency, long lifetimes, and low manufacturing costs. This has not yet been achieved for other thin-film technologies, but perovskite-based devices currently demonstrate enormous potential for achieving this.

29

09. Future of perovskites

Future research into perovskites is likely to focus on the reduction of recombination through strategies such as passivation and reduction of defects, as well as boosting efficiency through inclusion of 2D perovskites and better-optimized interface materials. Charge-extraction layers are likely to move away from organic materials to inorganic, to improve both efficiency and stability. Improving stability and reduction in the environmental impact of lead are likely to both continue to be significant areas of interest. Furthermore, as has been shown over the past few years - the engineering improvements of perovskite formulations and fabrication routines has led to significant increases in power conversion efficiency, with recent devices reaching over 23%, as of June 2018.

The rapid improvement of perovskite solar cells has made them the rising star of the photovoltaics world and of huge interest to the academic community. Since

their operational methods are still relatively new, there is great opportunity for further research into the basic physics and chemistry around perovskites. Whilst the

commercialisation of standalone perovskite solar cells still faces obstacles in terms of fabrication and stability. So, future of perovskites is improving day-by-day,

overcoming the disadvantages and boosting the efficiency through inclusion of 2D perovskites and better optimised interfaced materials. Charge extraction layers

are likely to move away from organic material to inorganic material in order to improve both efficiency band stability. This rapid improvement has made

perovskites as the rising star of photo voltaic world.

30

10. Summary

The versatility in the fabrication techniques of the perovskite light-absorbing layer, which include the solution-deposition method, vapour-deposition method,

and the vapour-assisted solution method, is attractive and such methods are also discussed.

Perovskite solar cells have developed rapidly, but some critical factors may restrict the development of perovskite solar cells. Firstly, the stability of the organic

lead halide perovskite is greatly affected by external environmental factors (such as humidity, temperature, and ultraviolet radiation), which lead to the low

stability of the devices and the great difficulties in encapsulating cells in the later stage. Therefore, the development of a high-stability device composition,

including the light-absorbing layer, electron/hole transport layer, and electrode materials, as well as the development of a simple and effective device-packaging

method, will be of great significance to promote the practicability of such devices. Secondly, the hole transporting material Spiro-OMeTAD used in perovskite

solar cells is expensive (10 times the market price of gold) and its synthesis process is complex. Therefore, it is necessary to design and synthesize new hole

transport materials to promote commercial applications of perovskite solar cells. Thirdly, it is difficult to deposit a large area of continuous perovskite film with

the traditional methods described above and so other methods should be improved to prepare high-quality and large-area perovskite solar cells for commercial

production in the future. Fourthly, the Pb element employed in perovskite solar cells is highly toxic, which will hinder the industrial promotion and development

of perovskite solar cells. Therefore, it is necessary to find a low-toxicity or nontoxic ingredient to replace Pb in the future. Fifthly, there is a lack of deep

understanding of the microscopic physics mechanism of perovskite solar cells. Therefore, it is necessary to establish a complete theoretical model to explain the

reasons for the increase in the conversion efficiency. Theoretical studies will not only help to further improve the performance of perovskite solar cells but also

provide ideas to develop simpler and/or more efficient new materials and structures. In a word, all the above issues need to be addressed before making full

application of the perovskite solar cells technology.

31

References[1] Perovskite. Webmineral

[2] W.A. Meulenberg, ... S. Roitsch, in Advanced Membrane Science and Technology for Sustainable

Energy and Environmental Applications, 2011

[3] Sarat Kumar Sahoo, ... Narendiran Sivakumar, in Perovskite Photovoltaics, 2018

[4] Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites ., M. M. Lee et al. , Science , Vol . 338 , p643–647 (2012).

[5] K. van Benthem, C. Elsässer and R. H. French (2001). "Bulk electronic structure of SrTiO3: Experiment and theory". Journal of Applied Physics. 90 (12): 6156. Bibcode:2001JAP....90.6156V. doi:10.1063/1.1415766

[6] Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9% ., H.-S. Kim et al., Scientific Reports, Vol 2 (2012).

[7] Enhanced charge carrier mobility and lifetime suppress hysteresis and improve efficiency in planar perovskite solar cells., S. H. Turren-Cruz et al., Energy & Environmental Science, Vol. 11 , p78–86 (2018).

[8] https://doi.org/10.1002/adma.202001981

[9] A.S. Bhalla, R. Guo and R. Roy, The perovskite structure – a review of its role in ceramic science and technology, Mat. Res. Innovat. 4, 3-26 (2000) and references therein

[10] Suneth C. Watthage, ... Michael J. Heben, in Perovskite Photovoltaics, 2018[11]Cava, Robert J. "Cava Lab: Perovskites". Princeton University. Retrieved 13 November 2013.

[12]^ Kendall, K. R.; Navas, C.; Thomas, J. K.; Zur Loye, H. C. (1996). "Recent Developments in Oxide Ion Conductors: Aurivillius Phases". Chemistry of Materials. 8 (3): 642–649. doi:10.1021/cm9503083.

[13]^ a b Munnings, C; Skinner, S; Amow, G; Whitfield, P; Davidson, I (15 October 2006). "Structure, stability and electrical properties of the La(2−x)SrxMnO4±δ solid solution series". Solid State Ionics. 177 (19–25): 1849–1853. doi:10.1016/j.ssi.2006.01.009.

[14]^ Munnings, Christopher N.; Sayers, Ruth; Stuart, Paul A.; Skinner, Stephen J. (January 2012). "Structural transformation and oxidation of Sr2MnO3.5+x determined by in-situ neutron powder diffraction" (PDF). Solid State Sciences. 14 (1): 48–53. Bibcode:2012SSSci..14...48M. doi:10.1016/j.solidstatesciences.2011.10.015. hdl:10044/1/15437.

[15]^ Amow, G.; Whitfield, P. S.; Davidson, I. J.; Hammond, R. P.; Munnings, C. N.; Skinner, S. J. (January 2004). "Structural and sintering characteristics of the La2Ni1−xCoxO4+δ series". Ceramics International. 30 (7): 1635–1639. doi:10.1016/j.ceramint.2003.12.164.

[16]^ Amow, G.; Whitfield, P. S.; Davidson, J.; Hammond, R. P.; Munnings, C.; Skinner, S. (11 February 2011). "Structural and Physical Property Trends of the Hyperstoichiometric Series, La2Ni(1−x)CoxO4+δ". MRS Proceedings. 755. doi:10.1557/PROC-755-DD8.10

32

M. A. Green, S. R. Wenham, J. Zhao, J. Zolper, and A. W. Blakers, “Recent improvements in silicon solar cell and module efficiency,” in Proceedings of the Twenty First IEEE Photovoltaic Specialists Conference - 1990 Part 2 (of 2), pp. 207–210, May 1990

J. M. Frost, A. Walsh, in Organic‐Inorganic Halide Perovskite Photovoltaics: From Fundamentals to Device Architectures (Eds: N.‐G. Park, M. Grätzel, T. Miyasaka), Springer International Publishing, Cham 2016, pp. 1– 17.

H. Kim, J. S. Han, J. Choi, S. Y. Kim, H. W. Jang, Small Methods 2018, 2, 1700310. Wiley Online Library Web of Science®Google Scholar 6G. Kieslich, S. Sun, A. K. Cheetham, Chem. Sci. 2015, 6, 3430. c.n.r Rao, in encyclopaedia of physical science and technology (third edition),2003 Managing global warming,2019 Sarat Kumar Sahoo, ... Narendiran Sivakumar, in Perovskite Photovoltaics, 2018 K. A. Muller & H. Burkard (1979). "SrTiO3: An intrinsic quantum paraelectric below 4 K". Phys. Rev. B. 19 (7): 3593–3602.

Bibcode:1979PhRvB..19.3593M. doi:10.1103/PhysRevB.19.3593 Quintero-Bermudez, R., et al. Compositional and orientational control in metal halide perovskites of reduced dimensionality. Nat. Mater.

https://doi.org/10.1038/s41563-018-0154-x (2018). S. Geller, Bul. Am. Phys. Soc. 30, 15 (1955). Woodhead Publishing Series in Electronic and Optical Materials 2019, M. Jaime, Rev. Mod. Physics 73, 583 (2001) and references therein. [34] E. Dagotto, Phase Separation and Colossal Magnetoresistance, (Berlin: Springer) 2002 and references therein. [35] B. Keimer et al., Editorial and contributions to the Focus on Orbital Physics, New J. Phys. 6 (2004) Kojima, Akihiro; Teshima, Kenjiro; Shirai, Yasuo; Miyasaka, Tsutomu (May 6, 2009). "Organometal Halide Perovskites as Visible-Light Sensitizers

for Photovoltaic Cells". Journal of the American Chemical Society 131 (17): 6050– 6051. doi: 10.1021/ja809598r.PMID 19366264 [13] Oxford Photovoltaics (June 10, 2013) Oxford PV reveals breakthrough in efficiency of new class of solar cell. [14] Sivaram, Varun; Stranks, Samuel D.; Snaith, Henry J. "Outshining Silicon". Scientific American (July 2015): 44–46 [15] Snaith, Henry J. (2013). "Perovskites: The Emergence of a New Era for Low-Cost, High-Efficiency Solar Cells". The Journal of Physical Chemistry Letters 4 (21): 3623–3630.doi:10.1021/jz4020162

33

List of figuresFigure 2.1- perovskite lattice arrangement

Suneth C. Watthage, ... Michael J. Heben, in Perovskite Photovoltaics, 2018Fig. 2.2- The perovskite mineral structure

Sarat Kumar Sahoo, ... Narendiran Sivakumar, in Perovskite Photovoltaics, 2018

Fig – 2.3 strontium titanate

K. van Benthem, C. Elsässer and R. H. French (2001). "Bulk electronic structure of SrTiO3: Experiment and theory". Journal of Applied Physics. 90 (12): 6156. Bibcode:2001JAP....90.6156V. doi:10.1063/1.1415766

Fig. 3.2 - some major milestones in the progress

3. How to Make over 20% Efficient Perovskite Solar Cells in Regular (n-i-p) and Inverted (p-i-n) Architectures ., M. Saliba et al ., Chemistry of Materials, Vol. 30, p4193–4201 (2018).

4. Perovskites photovoltaic solar cells: An overview of current status. , P. Tonui et al. , Renewable & Sustainable Energy Reviews, Vol. 91 , p1025–1044 (2018).

Fig. 3.2 shows some major milestones in the progress of PSCs,

Suneth C. Watthage, ... Michael J. Heben, in Perovskite Photovoltaics, 2018

Fig 3.3- structure of cubic perovskite of PSCs rontium titanite

[10] Fig – 2.2.1 layers of perovskites

Figure 3.1 - Example of a unit cell of the perovskite structure: the case of CaTiO3.

Fig 4 – classification of perovskite

Fig 4.1- layered perovskites

Fig 4.2 cubic perovskites

Fig 4.3- double layered perovskites

Fig 4.4- perovskite light absorber

Fig 4.5 - manipulation of perovskites

Fig.6 Conditions required for ferroelectricity (polarization) and ferromagnetism (unpaired electron spin motion)

Fig 7.1 - processing of perovskite solar cell

FIG 7.2- EVOLUSTION OF PEROVSKITES

FIG 7.3- PROCESSING POF DIFFERENT MATERIALS

FIG 7.4 - LASER

34

35