I2CamQuantun Dot and Perovskite Solar Cells · TiO2- CdSe Assembly Using a Bif unctional Linker Molecule TiO2 TiO2 CdSe TiO2/CdSe 2.3 nm 2.6 nm 3.7 nm 3.0 nm Baker & Kamat Langmuir

1

Prashant V. Kamat

Dept Of Chemistry and Biochemistry and Radiation Laboratory

University of Notre Dame, Notre Dame, Indiana 46556-0579

Quantum Dot and Perovskite Solar Cells

http://www.nd.edu/~kamatlabOR Kamatlab.com

http://www.bloomberg.com/news/articles/2016-06-13/we-ve-almost-reached-peak-fossil-fuels-for-electricity

….. a Solar Wave

2

Progress in Photovoltaics: Research and Applications 2017, 25, 3-13.

Photovoltaic Advances

Can we address clean energy

challenge with Nanotechnolgy?Perovskite[22.7%]QDSC[13.4%]

Thin Film Solid State Solar Cells

- Solution processable

- Low temperature

processing

- Bench-top technology

- Low energy demand

for production and

hence GHG2013, 47, 3482

3

Early Years1970 -1990

Oil crisis (OPEC oil embargo) of 1973 brings awareness of Renewable Energy

Artificial Photosynthesis was coined to mimic photosynthesis-Photoinduced Electron Transfer Reactions

Semiconductor Photoelectrochemistrybecomes a popular research topic

Photocatalytic properties of semiconductor particle systems emerge

Fujishima

Honda

4

Exploring Semiconductor Nanoparticles forLight Energy Conversion

Chemical Energy(Solar Fuels)

Environmental Remediation

Electricity(Solar Cells)

Colloids to Nanoparticles(1991-2002)

Nature 1991, 353, 737-740

5

Energy (eV)

2.0 2.5 3.0 3.5 4.0

Lum

ine

scen

ce Absorb

ance

10K 45Å

27Å

22Å

19Å

16Å

13Å

12Å

Colloidal Quantum DotsCdSe

Murray, C.; Norris, D.; Bawendi, M., Synthesis and characterization of nearly monodisperse CdE (E=S, Se, Te) semiconductor. J. Amer. Chem. Soc. 1993, 115, 8706-8715

Courtesy: M. Kuno

http://tastyresearch.files.wordpress.com/2007/08/opposites_attract.jpg10

A brief word on quantum confinement

h+ e-

• ‘Quantum confinement’ – when the material dimensions are comparable to or smaller than the e and h Bohr radii

• e and h have their own characteristic Bohr radius

• Differ slightly due to their different effective masses in the bands

Kuno, M. K. Introductory Nanoscience: Physical and Chemical Concepts. 2012

weakintermediate

strong

∝ 1/ for QDs

6

"The technology works by harnessing nano crystals that range in size from 2 to 10 nanometers. Each dot emits a different color depending on its size. By adding a film of quantum dots in front of the LCD backlight, picture color reproduction rate and overall brightness are significantly improved."

http://www.cnet.com/news/lg-leaps-quantum-dot-rivals-with-new-tv/

<$1000

Quantum Dot Solar Cells

Tunable band edge Offers the possibility to harvest light energy over a wide range of visible-ir light with selectivity

Hot carrier injection from higher excited state (minimizing energy loss during thermalization of excited state)

Multiple carrier generation solar cells.Utilization of high energy photon to multiple electron-hole pairs

7

Three Major Aspects of QD Solar Cells

• Tuning properties of Nanomaterials

• Surface modification

• Assembly on Electrodes

• Photon Capture (Light Absorption)

• Excited State Dynamics

• Charge Separation • ETL & HTL to capture charges


• Efficiency

Synthesis & Characterization

Photochemistry & Photophysics

Electrochemistry & Photoelectrochemistry

Designing Quantum Dot Solar Cells

8

Polymer-SemiconductorHybrid Cell

Semiconductor Hetero- junction Solar Cell

Quantum Dot Senistized Solar

Cell

PEDOT/PSS

P3HT/SC Nanocrystals

Deposition of QD Films

TiO2 CdSe

SILAR

ElectrophoreticdepositionChemical

bath

Drop cast/spin coat

Molecular linker

Cd2+

precursorSe2- or S2-

precursorOTE/TiO2/CdSe

or (CdS)OTE/TiO2

ea

bd

c

Experimental Approach

Synthesis of QDs by Hot-Injection Method

1-8 Cycles CdSe SILAR

9

TiO2- CdSe Assembly Using a Bifunctional Linker Molecule

TiO2

TiO2CdSe TiO2/CdSe

2.3 nm 2.6

nm3.7 nm

3.0 nm

Baker & Kamat Langmuir 2010, 26, 11272-11276.

Designing Nanostructured Hybrid Assemblies for Harvesting Light Energy

The reactivity of semiconductor surface can be used to tailor the property of nanocrystals

10

19

Liquid Junction

Solid State

Optically Transparent Electrode

Substrate (Metal Oxide)

Sensitizer

Electrolyte / Hole Conductor

Counter Electrode

Anatomy of a Quantum Dot Solar Cell

350 400 450 500 550 600 650 700

0

10

20

30

40

50 (A) 3.7 nm 3.0 nm 2.6 nm 2.3 nm

Wavelength (nm)

IPC

E (

%)

350 400 450 500 550 600 650 700

0

10

20

30

40

50 (A) 3.7 nm 3.0 nm 2.6 nm 2.3 nm

Wavelength (nm)

IPC

E (

%)

Tuning the Photoresponse of QDSC

h

e

O

R

CdSeTiO2

VB

CB

ee

e

hh h

O

e

h

R

E

IPCE or Ext. Quantum Eff.= (1240/) x (Isc/Iinc) x 100

• Size selective deposition of CdSe QDs to TiO2 films

• Ability to tune the photoresponse of QDSC

• Higher efficiency with smaller size QDs

11

0.0 0.1 0.2 0.3 0.4 0.5 0.60

5

10

15

20

Cur

rent

Den

sity

(m

A/c

m2 )

Voltage (V)

Pt RGO-Cu

2S

RGO-Cu2S (Binder)

400 500 600 700 8000

20

40

60

80

100

IPC

E (

%)

Wavelength (nm)

RGO-Cu2S

RGO-Cu2S (Binder)

TiO2/CdSe/CdS PhotoanodeCu2S/Graphene Electrode1M Na2S, 0.1 M S in water100 mW/cm2 Area 0.25 cm2

Voc =0.55 VIsc = 18 mA/cm2

ff = 0.5

= 4.4 %

Binder: poly(vinylidene) fluoride (PVDF)

QDSC Performance with Cu2S/Graphene Counter Electrode

2011, 2, 2453–2460

Towards the design of Rainbow Solar Cell…. semiconductor QDs in a tandem fashion

• To broaden the photoresponse of QDSC

• To explore the synergy of layered QDs in capture and conversion of incident photons

• To minimize the energy loss associated with higher energy excitations

12

• Bandgap can be tuned by varying S:Se composition

• Emission Quantum yield of CdSeS is as high as 0.62

• CdSSe has been shown to have graded alloy structure

• Inject electrons into metal oxide semiconductors and can be employed in QDSC

• Enables design of Tandem layered QDSC

CdSSe quantum dots

Santra & Kamat JACS 2013, 135, 877–885

Electrophoretic Deposition of QDs

Sequential vs. Mixed

• Semiconductor QDs in mixed solvents become charged and can be driven to the electrode surface with an externally applied bias.

• Following the increase in absorption, one can quantitatively deposit QDs within mesoscopic TiO2 film

2013, 135, 877−885

13

Photovoltaic performance of tandem layered quantum dot solar cells

Expt Calc.

Green + Red 2.49 2.14

Orange + Red 3.19 2.44

Green + Orange + Red 3.00 2.13

Green, Orange, Red (Mixed) 2.34 2.40

Santra and Kamat, JACS 2013, 135, 877–885

Sequential vs. Mixed

ee

e

h h h

e(TiO2)CB

VB

EF

TiO2CdSeS

Green Orange Red

ee

e

h h h

e(TiO2)CB

VB

EF

TiO2CdSeS

Green Orange Red

Coupling energy and electron transfer at mesoscale

Exciton Recycling in Graded NanocrystalStructuresFrenzl et al., Nano Lett. 2004, 4, 1599-1603

- Optical excitons efficiently transfer along the bandgap gradient

- The graded structure facilitates captures otherwise trapped and lost electron-hole pairs

2017, 2, 391−396

14

Evolution of Thin Film Solar Cells

3623−3630

DOI: 10.1021/acs.jpclett.5b02524

Our recent paper showing TiO2 charging effects

http://pubs.acs.org/doi/pdfplus/10.1021/jacs.7b10958

Our recent paper showing TiO2 charging effects

http://pubs.acs.org/doi/pdfplus/10.1021/jacs.7b10958

Late 1990s - Early 2000s: The Mitzi Era

David Mitzi - IBM: T. J. Watson Research Center

1. (C4H9NH3)2(CH3NH3)n-1SnnI3n+1

2. [NH2C(I)=NH2]2(CH3NH3)mSnmI3m+2

3. (C4H9NH3)2MI4 (M = Ge, Sn, Pb)

4. (C4H9NH3)2EuI4

5. (NH2CH=NH2)SnI3

1. D. B. Mitzi, C. A. Feild, W. T. A. Harrison, and A. M. Guloy, Nature, 1994, 369, 467–469.2. D. B. Mitzi, S. Wang, C. a Feild, C. a Chess, and a M. Guloy, Science, 1995, 267, 1473–6.3. D. B. Mitzi, Chem. Mater., 1996, 8, 791–800.4. D. B. Mitzi and K. Liang, Chem. Mater., 1997, 9, 2990–2995.5. D. B. Mitzi and K. Liang, J. Solid State Chem., 1997, 134, 376–381.6. D. B. Mitzi, K. Chondroudis, and C. R. Kagan, IBM J. Res. Dev., 2001, 45, 29–45

4

Explored Applications inOLEDand Transistors

15

2006-2009: Early Developments

A. Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, 210th ECS Meeting, 2006.A. Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, 212th ECS Meeting 2007.A.Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, J. Am. Chem. Soc., 2009, 131, 6050–1.Im J. H. et al Nanoscale 2011, 3, 4088−4093.

2006-2008• Miyasaka reports liquid-junction CH3NH3PbI3 and CH3NH3PbBr3 solar

cells at several conferences• Efficiency ranges from 0.3% - 2.2%

2009• Miyasaka et al. report first peer-reviewed perovskite solar cell• Low stability (several min.)2011Park, N.-G. Perovskite Quantum-Dot-Sensitized Solar Cell.

Sensitizer JSC

(mA/cm2)VOC (V) FF η

(%)

CH3NH3PbBr3 5.57 0.96 0.59 3.13

CH3NH3PbI3 11.0 0.61 0.57 3.81

2012: Emergence of Perovskite Solar Cell

1. A. Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, 214th ECS Meeting 2008.2. H.-S. Kim, et al. Sci. Rep., 2012, 2, 591.3. M. M. Lee, J. Teuscher, T. Miyasaka, T. N. Murakami, and H. J. Snaith, Science, 2012, 338, 643–647.

• Initial attempt in 2008 with polypyrrole1

• Spiro-OMeTAD as HTM: A Landmark Development

Received May 31, 2012

Received July 5, 2012

9.7% 10.9%

Published August 2012

Published October 2012

16

SCIENCE 2012, 338 , 643.Nature 2013, 499, 316-319

Organic-Metal Halide Perovskites1.Mix PbI2 and methyl

ammonium iodide in chlorobenzene and stir for 2 hours at 70 °C –yellow colored solution

2. Spin coat the solution onto electrode surface kept on a hot plate (70-80 C)

3. The film turns black as it crystallizes into pervoskite structure

4. Make metal contact

CH3NH3PbI3 Solar Cell with 16% Efficiency

32

1 μm

0 0.2 0.4 0.6 0.8 1.00

5

10

15

20

25

Steady-state current @ 0.85 V (averaged over 30 s) Average of forward & reverse scans

Forward:

Jsc

= 22.4 mA/cm2

VOC

= 1.01 V

ff = 0.66 = 15.0%

Voltage (V)

Cu

rre

nt

De

ns

ity

(m

A c

m-2)

Reverse:

Jsc

= 22.4 mA/cm2

VOC

= 1.04 V

ff = 0.73 = 17.0%

Area = 0.13 cm2

300 400 500 600 700 8000

10

20

30

40

50

60

70

80

90

100

Wavelength (nm)

EQ

E (

%)

0

5

10

15

20

Inte

gra

ted

Cu

rren

t D

ensi

ty (

mA

cm

-2)

2-step deposition of MAPbI3 onto mp-TiO2 (~200 nm thick)

17

Best Solar Cell Certified EfficienciesThe PSCs fabricated with LBSO and methylammonium lead iodide (MAPbI3) show a steady-state power conversion efficiency of 21.2%, versus 19.7% for a mp-TiO2 device.

CsPbX3 Perovskite Quantum Dots

• Highly luminescent QDs

• CsPbX3 perovskites are seen as a more stable alternative to MAPbX3 species.

• Ease of synthesis and control of surface chemistry

• Features a cubic perovskite structure and broad spectral control through size and composition.

Kulbak, M. et al. J. Phys. Chem. Lett. 2016, 7 (1), 167–172.

Guria et al., ACS Energy Lett. 2017, 2, 1014−1021.Eperon, G. E. et al. J. Mater. Chem. A 2015, 3 (39), 19688–19695.

34

18

Experimental Approach

QD Synthesis

Spectroscopy

Assembly

PbBr2, OctadeceneOleic acid, Olylamine

Cesium Oleate

120 °C

DOI: 10.1021/jacs.6b04661

2016,138, 8603–8611

DOI: 10.1021/acs.chemmater.7b03751

How Layer-by-layer deposition of CsPbBr3 QDs provide uniform perovskite films

19

The Thickness Dependence

The PCE of the solar cells increases with CsPbBr3 thickness until 250 nm140 nm 340 nm

The AX treatment strategy provides a general method for tuning the electronic properties of the CsPbI3QD films.

FAI coating yields a doubling of the already-high mobility of CsPbI3QD films and results in a certified record PCE of 13.43% - above the best reported PCE for dye-sensitized solar cells, organic PVs, and CZTSSe PV technologies

Sci. Adv. 2017;3: eaao4204 27 October 2017

20








• Efficiency




Q: How can we probe the charge carriers generated in semiconductors and track interfacial charge transfer?

Ans. Employ Spectroscopy Tools to identify deactivation of excited state (e.g., emission)

Monitor absorption changesIdentify products

h

et ht

VB

–

+

+

–CB

A−

A

B+

B

21

h

et ht

VB

–

+

+

–CB

A−

A

B+

B

pump

probeEn

Time-resolved absorption and emission spectroscopy is a convenient technique to probe photoinduced processes

Bandgap Excitation

Emission Spectroscopy

- Directly provides lifetime of the excited state

- Establishing radiative and non radiative decay pathways

- Can also provide information on competing processes (e.g., interfacial electron transfer

h

et ht

VB

–

+

+

–CB

B+

B

22

ExamplesProbing excited state dynamics

ZnO

CdSe

Bandgap versus Sub-Bandgap Transitions

23

CdSe + h CdSe (e-h)

CdSe (e+h) kr CdSe

CdSe (e+h) knr CdSe

CdSe (h) + S2- kht CdSe + S-.

Probing hole transfer

= 1/(kr+knr)

’ = 1/(kr+knr+kht)

1/’ -1/=(kr+knr+kht) - (kr+knr)= kht

Thus one can estimate the rate constant of charge transfer by estimating lifetimes with and without the acceptor

Transient Absorption Spectroscopy

∆Abs = Abs(Pump + probe) – Abs(Probe) = Absexcited state – Absground state

24

47

Femtosecond Transient AbsorptionΔAbs = Abs(Pump + probe) – Abs(Probe) = Absexcited state – Absground state

1000 ps100 ps10 ps1 ps0 psWavelength (nm)

Abs

orba

nce

1000 ps

0 ps

Time (ps)

ΔA

0

Steady State Absorption

Transient Absorption

ProbeProbe

ProbeProbeProbeProbeProbe ProbeProbeProbeProbeProbe

VB

CB

Ox

Redh

et ht

VB

–

+

+

–CB

TiO2

CdSe

h

e

O

R

Photoelectrochemistry

pump probe

detector

Spectroscopy

GERISCHER H, LUBKE MA PARTICLE-SIZE EFFECT IN THE SENSITIZATION OF TIO2 ELECTRODES BY A CdS DEPOSITJOURNAL OF ELECTROANALYTICAL CHEMISTRY 204 (1-2): 225-227 1986

25

450 500 550 600 650

-0.08

-0.04

0.00B

CdSe-MPAA

Wavelength, nm

1 ps 35 ps 400 ps 1500 ps

450 500 550 600 650

-0.08

-0.04

0.00B

CdSe-MPAA

Wavelength, nm

1 ps 35 ps 400 ps 1500 ps

Charge Separation in TiO2/CdSe (3 nm)

CdSe

VB

CBe

h

pump

probe

detector

450 500 550 600 650

-0.08

-0.04

0.00

C

CdSe-MPA-TiO2

A

Wavelength, nm

1 ps 35 ps 400 ps 1500 ps

450 500 550 600 650

-0.08

-0.04

0.00

C

CdSe-MPA-TiO2

A

Wavelength, nm

1 ps 35 ps 400 ps 1500 ps

TiO2

k= 1.95x1011 s-1

CB

VB

0 200 400 600 800 1000 1200 1400-1.00

-0.75

-0.50

-0.25

0.00

No

rmal

ized

tra

nsi

ent

ble

ach

Wavelength, nm

CdSe-MPA CdSe-MPA-TiO2

Time, ps

I. Robel; M. Kuno; P. V. Kamat, J. Am. Chem. Soc. 2007, 129, 4136-4137. K. Tvrdy; P. A. Frantsuzov; P. V Kamat, Proc. Natl. Acd. Sci. USA 2011, 108, 29-34.

• Electron transfer in QDSCs has been widely studied many research groups

• Not the limiting factor in solar cell performance in most cases

ket= 107 s-1 ket= 1.2x1010 s-1

CdSe2.4 nm

CdSe7.5 nm

TiO2

ee

• Follows Many-State Marcus Theory

26

V. Chakrapani; D. Baker; P. V Kamat, J. Am. Chem. Soc. 2011, 133, 9607-9615.

Time-resolved emission spectroscopy

Rate constants:

kht ~ 107-109 s-1 vs. ket ~ 1010-1011 s-1

Hole transfer as a limiting factor

Christians and Kamat ACS Nano 2013, 7, 7967–7974

Fill factor 0.59Efficiency 3.3%,

Sb2S3/CuSCN Based Solid State Solar Cells

27

Sb2S3(h) Sb2S2S−•

460 nm

560 nm

1. Hole Trapping in Sb2S3 Films

The hole trapping process proceed s with a rate constant of 4.5 × 1011 s-1.

Establishing Two Step Hole Transfer Process

Sb2S2S−• + e Sb2S3 + heat Sb2S2S−• + CuSCN Sb2S3 + CuSCN(h)

2. Hole Transfer to CuSCN

Hole transfer to CuSCN occurs with a rate constant of = 5.9 × 108 s-1

• The transfer of photogenerated holes from the absorber species to the p-type hole conductor is a two step process and plays a critical role in the charge separation process.

• Hole transfer is 2-3 order of magnitude slower than the electron injection process

Establishing Two Step Hole Transfer Process

ACS Nano 2013, 7, 7967–7974

28

®

55

• kht strongly depends on Sb2S3 film thickness

(1) Trapping: Sb2S3(h)

Sb2S2S−•

(2) Diffusion: Sb2S2S−• + CuSCN

[Sb2S2S−•−CuSCN]

(3) Transfer: [Sb2S2S−•−CuSCN]

Sb2S3 + Cu(SCN−•)

J. A. Christians; D. T. Leighton Jr.; P. V. Kamat, Energy Environ. Sci. 2014, 7, 1148-1158.

Investigating Hole Diffusion

Solar Cell Characterization








• Efficiency




29

Fermi Level

• The Fermi level is a pseudo-state that has a 50% probability of being occupied– A measure of the potential energy of an

electron in a solid

-

+ + +

- -CB

VB

- - -

+ + +

CB

VB

-

+ + +

CB

VB

CB- - -

VB

+

Bard, A. J., Electrochemical Methods

Introduction 2-Electrode 3-Electrode Other Conclusions

CB

VB

Semiconductor Heterojunctions

CB

VB

- -

+

-

+ + +

--? ?-


30

Band Bending in Semiconductors

Formation of space charge layer

Band bending determines maximum photovoltage

Band bending can be tuned by varying redox couple



31

1. Illuminate Solar Cell– 100 mW/cm2, Air Mass 1.5G solar irradiation

2. Measure current at different voltage output

3. Simulates possible “real world” operating conditions

4. Gives us Power Conversion Efficiency

Current-Voltage Measuremnts (I-V curves)


Recombination and VOC

Po

ten

tial

+

-

FTOTiO2

CdSe

S2-/Sn2-

EFerm

i Cu2S/RGO

Desired ElectronTransfer

Recombination

Step by Step:1. Excitation

2. Electron Transfer

3. Recombination

4. Build up e- in CB until Rexcitation = Rrecombination

5. If recombination rate is increased, VOC is decreased

VOCVOC

1

2

34

5


32

In the Dark (at Equilibrium)

FT

O

Cu2

S/R

GO

i

- +

Eappl

Po

ten

tial

+

-

FTOTiO2

CdSe

S2-/Sn2- Cu2S/RG

EFermi

-+

Hodes, G., Gratzel, M. et. al, J. Phys. Chem. B, 2000, 104, 2053-2059

S2-/Sn2-

TiO2/CdSe


Let There Be Light!

Po

ten

tial

+

-

FTOTiO2

CdSe

S2-/Sn2-

∆V = Efermi - Ecounter

Eappl = - Voc i = 0Eappl > -Voc i < Jsc

Eappl= 0 V i = Jsc

Cu2S/RG

EFermi ∆V

Hodes, G., Gratzel, M. et. al, J. Phys. Chem. B, 2000, 104, 2053-2059

FT

O

Cu2

S/R

GO

i

- +

Eappl

-+

S2-/Sn2-

TiO2/CdSe


33

Quantum dot architectures forlight energy conversion are still inplay. Ternary and quaternarysemiconductor QDs offer newopportunities.

Excited state charge transfer andtransport dictate the solar cellperformance.

Proper methodology should beimplemented for characterizationof solar cells

Summary

Kamat, P. V.; Christians, J. A.; Radich, J. G. Quantum Dot Solar Cells. Hole Transfer as a Limiting Factor in Boosting Photoconversion Efficiency (Review). Langmuir 2014, 30, 5716–5725.

Manser, J. S.; Christians, J. A.; Kamat, P. V. Intriguing Optoelectronic Properties of Metal Halide Perovskites. Chem. Rev. 2016, 116, 12956–13008.

Kamat, P. V. Semiconductor Surface Chemistry as Holy Grail in Photocatalysis and Photovoltaics. Acc. Chem. Res. 2017, 50, 527-531.

What will the future hold?

Over the last twenty years, the per-kWh price

of photovoltaics has dropped from about $500 to ~ $1; think of what the

next twenty years will bring.

It is Sun-Believable

Documents

I2CamQuantun Dot and Perovskite Solar Cells · TiO2- CdSe Assembly Using a Bif unctional Linker Molecule TiO2 TiO2 CdSe TiO2/CdSe 2.3 nm 2.6 nm 3.7 nm 3.0 nm Baker & Kamat Langmuir