Crystalline Zinc Indium Selenide thin film electrosynthesis

and

its photoelectrochemical studies

By

Anuradha Bhalerao-Pawar, B.G. Wagh, N.M. Shinde, S. B.

Jambure, C.D.Lokhande

K.K.Wagh Institute of Engineering Education & Research, Nasik

K.K.Wagh Arts, Commerce & Science College, Pimpalgaon Nasik.

Department of Physics, Shivaji University, Kolhapur.

Outline

1. a. Thin Film Science andb. Thin Film Deposition Techniques

2. Electrodeposition of Zinc Indium Selenide Thin films

3. Structural Analysis of Thin Film

4. PEC Study of Thin Film

Third Dimension Negligibly

Smaller

Two Dimensional

Solids

Thickness less than 100nm

Thin Film

1a. Thin Film Science

When Thickness is comparable with Mean Free Path of Electrons

Rigidity & TransparencyAlters with thickness

Effect of Film Thickness on Material Properties

Resistivity & Dielectric constants Vary as a function of thickness

Biological Deposition :Use of Biological

Reaction

Hybrid Deposition: Mixing of Above

Techniques

Physical Deposition :One of the Physical

Properties is Altered

Chemical Deposition: Use of Chemical

Reaction

Electrochemical Deposition

1b. Thin Film Deposition Techniques

• Experimental set upconsists of :

1. Anode

Counter Electrode (C)

2. Cathode

Working Electrode (W)

3. A Suitable Electrolyte.

• When electric currentpassed through electrolyte:

Ionic movement starts

Experimental Set-Up

Positive ions deposit on cathode forming a thin film.

The amount of material electroplated depends upon: The direction of current existing at particular region of electrode.

Charge Transfer across Electrode and Electrolyte

causesCharge Cloud formation near

the Electrodes

W------

C++++++

+++- - -

- +-++ ----+

The uniform current distribution : A uniform film.

Experimental Mechanism

2.Electrodeposition

of Zinc Indium Selenide Thin Films

Experimental Details

Working Electrode

Electrolyte: ZnSo4 (0.2M), InCl3 (0.02M) and SeO2 0.002M)

Counter Electrode

Reference Electrode

Stainless Steel Plate with Surface Treatments

Graphite RodStandard Calomel

Electrode (SCE)

Temperature : Ambient

Potential :-600mV

pH : 2.2

Potential Optimization

5

4

3

2

1

0

ZnSO4

InCl3

SeO2

ZnSO4+InCl3+SeO2

Potential Vs SCE (mV)C

urre

nt D

ensi

ty (m

A/c

m2 )

a

b

c

d

0 200 400 600 800 1000

The polarization curves for reduction of (a) zinc, (b) indium,(c) selenium and (d) for the bath containing precursor solutions

3.Structural Analysis

10 20 30 40 50 60 70 80

200

400

600

800

1000

(116

)

(Su

bst

rate

)

(400

)(301

)(220

)

(112

)

Inte

nsi

ty (

A.U

.)

Degree)

ZnIn2se4 Data

JCPDS File No. 39-1156

The X-ray diffraction pattern of as-deposited ZnIn2Se4 thin film showsTetragonal crystal structure with remarkable growth along (220) plane

Surface Morphology

The scanning electron micrographs of ZnIn2Se4 film electrodeat magnification 10,000 over growth observedAnd at 30,000 magnification : Well resolved uniform grain growth observed. Local edge sharing rod like structure observed with breadth in nanorange (500nm )

1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.40

30000

60000

300 400 500 600 700 800

% A

bs

orb

an

ce

Wavelength () (nm)

Absorbance

h

x 10

-11 (e

V/c

m)2

h(eV)

Inset shows : Material shows good absorbance in wavelength region 400-500nmEnergy band gap of the material : 2.4eV

Blue Shift of 0.1eV

Optical Absorbance Study

4.Photo Electrochemical [PEC] Study of Thin Film

PEC CellSolid – Electrolyte Junction

Photoelectrosynthetic Cell

Free Energy Change Non Zero

Electrochemical Photovoltaic Cell (ECPV Cell)

Free Energy Change = 0

Photo Electrode(Thin Film)

Electrolyte Counter Electrode

Use of Zinc Indium Selenide Thin Film as Photo Electrode in S-E Junction

+

++

++

++

+-

-

-

-

-

-

-

- ----------

Bulk

ElectrolyteSemiconductor

Space Charge Ionized Group

Helmholtz Double Layer

Solid- Electrolyte Junction

Barrier is Formed due to Transfer of Majority

Carriers from Semiconductor to

Electrolyte

Major Potential Drop in Semiconductor Space

Charge Layer.

Only small fraction of Drop in Electrolyte Region

ECPV Cell : Action at Photo electrode

Photo electrode Exposed

Electron-Hole Pairs Generated in Depletion

Region

Electrons move from Photo anode to Counter

Electrode

E-H Pair Driven Apart by Electric Field at Interface

(Photo voltage)

Holes react with Electrolyte and Redox completes at CE

Photoelectrochemical Cell output parameter

-600 -400 -200 0 200 400 600

-200

-100

0

100

200

Light

DarkC

urre

nt

De

ns

ity

(

A/c

m2)

Voltage (mV)

Dark Current

Light Current

-750 -500 -250 0 250 500-1000

-750

-500

-250

0

250

Cu

rre

nt

De

ns

ity

(A

/cm

2)

Voltage (mV)

Chopping

Dark Current

Light Current

Dark

Light

The Current–voltage (I–V) characteristic in dark and under light illumination (a) photovoltaic power output characteristics : Isc=0.05mA/cm2 Voc=250mV(b) light chopping : n-Type conductivity (magnitude of voltage increases with negative polarity towards Zinc Indium Selenide electrode

Speed of response and Transient photoresponse characteristics

20 40 60

5

10

15

20

Cu

rre

nt

(A

)

Time (S)

Light

Dark

Chopping

20 40 60

-285

-280

-275

-270

Vo

lta

ge

(m

V)

Time(S)

Voltage

Speed of Response Photo induced voltage as a function of time

Capacitance–voltage (C–V) characteristics

Mott–Schottky plot of PEC cell.

Electrochemical Impedance Spectroscopic (EIS) Study

0 2000 4000 6000 8000 10000-500

0

500

1000

1500

2000

2500

3000

3500

-Z'' (

Oh

m)

Z' (Ohm)

Raw data

Fitted data

Nyquist plot for ZnIn2Se4 electrodeEquivalent circuit derived

fromNyquist plot

Component values of equivalent circuit

Parameter Value Error

(1) Rs49 Ω 6.4

(2) R11019.19Ω 10743.32

(3) C10.002484 F 0.047381

(4) R28431.614Ω 11644.95

(5) Qy26.74E-05F 2.54E-05

(6) Qa20.838F 0.0764

Conclusion

1. X-ray Diffraction Analysis: Tetragonal Crystal Structure

2.SEM Analysis : Homogeneous local edge sharing network structure

3.Optical Absorbance study :Direct band gap semiconducting material

4. Photovoltaic Power output characteristics: Photosensitive material Used as Buffer layer in photovoltaic device

5.Speed of Response and Transient Photo response :Use of this material as light sensorStability of electrode

7.Mott-Schottky plot : Flat Band Potential : -0.8 V/SCE

Acknowledgement

1.Contribution of Pune University Research Fund under BCUD scheme

2. Motivation ofK.K.Wagh Institute of Engineering Education and

Research, Nasik

Thanks

1. ICAER Co-ordination Committee

2. Energy Angels