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
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