Sin Khai Wen FYP Viva Presentation

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Final Year Project 2015/2016
Final Year Project Title:
Deposition and Characterization of CdSe Nanoparticles Multilayer on
Conductive Substrate by Chemical Bath Deposition
Final Year Project Viva Presentation
Name: Sin Khai Wen
No. Matric: 116541
Supervisor: Dr. Khatijah Aisha Bt. Yaacob

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Introduction of CdSe
• Important II-VI compound because of its size-dependent exceptional optoelectronic properties in the visible range
• It has a direct bulk band gap (1.74 eV) with high absorption coefficient near the band edge, high photosensitivity, tunable band
gap from around 450 to 700nm which cover the entire visible spectral range and quantum size effect, allow its use in thin film
devices, especially for application in solar hybrid system.
• Solar cell, light emitting diode, nano sensors, photo detectors
Figure 1: Left, absorption spectra of differently sized CdSe nanocrystals. Right, corresponding PL spectra representing deeper red, red, orange, yellow,
green and blue (from right to left) emitting CdSe cluster and nanocrystals under UV excitation at 380nm (Yuan & Krüger, 2012)
Yuan, Y. & Krüger, M., 2012. Polymer-Nanocrystal Hybrid Materials for Light Conversion Applications. Polymers, Volume 4, pp. 1-19.

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Introduction of Chemical Bath Deposition
• Chemical bath deposition (CBD) is the simplest deposition technique that do not require sophisticated and costly instruments.
• Extensively used for preparation of CdSe thin film because of its application as window layer material in solar cell fabrication
• Chemical Reaction:
Cadmium salt reacted with NTA to form complex Cd salt,
Cd2+ + NTA [Cd(NTA)]2+ (1)
Hydrolysis of potassium hydroxide in water gives OH- ions in solution according to the equation,
KOH(s) + H2O(l) K+ (aq) + OH- (aq) + H2O (l) (2)
Hence, from reaction of (1) and (2), it will give solid Cd(OH)2 formation.
Cd2+ + 2OH-  Cd(OH)2 (s) (3)
From the reaction of selenium and sodium sulfite, we will get equation (4), and when dissolving in [Cd(NTA)]2+ solution, the byproduct is (5)
Na2SO3 + Se Na2SeSO3 (4)
SeSO3
2- + OH- HSe- + SO4
2- (5)
The overall reaction can be described as follow
Cd(OH)2 (s) + HSe- CdSe + OH- + H2O (6)
,

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Introduction of QDSSC
Figure 2: Operating principle of a typical QDSSC
(Jun, et al., 2013)
• The electrons will enter into the conduction band (CB) of the QD
and the hole remains in the valence band (VB).
• The excited QD injects the electron from its CB into the CB of the
wide band gap semiconductor (e.g. TiO2) and become oxidised.
• The injected electron from the QD percolates through the porous
TiO2
, reaches the conducting glass, travels through the external
load, completes the circuit.
• The oxidized QD is then restored (hole is filled with electron)
when it is reduced by S2- from the electrolyte and in turn it is
oxidized into S2- that diffuses to the counter electrode.
Jun, H., Careem, M. & Arof, A., 2013. Quantum dot-sensitized solar cells-perspective and recent developments: A review of Cd chalcogenide quantum dots as sensitizers. Renewable
and Sustainable Energy Reviews, Volume 22, pp. 148-167.

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Problem Statement
• The deposition process in CBD uses a controlled chemical reaction which result in
the deposition of a nanocrystalline films by precipitation
• Small crystal size leads to quantum size effect and increase in the optical band gap
• The major problem of the CBD method is the difficulty to produce small CdSe
nanoparticle on the substrate
• Another problem is deposition of CdSe multilayer with different size of CdSe
nanoparticles on the substrate

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Research Objectives
• To synthesis different CdSe nanoparticle size using chemical bath deposition
method by changing parameters such as complex agent concentration.
• To deposit two layer of CdSe nanoparticles with different particle size on fluorine
doped tin oxide(FTO) substrate.
• To determine and compare electrical properties of CdSe multilayer with CdSe
single layer solar cell.

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Methodology- Procedure
FTO cleaning – 2-propanol Deposition of TiO2 mesoporous layer Deposition of CdSe on the
mesoporous TiO2 thin films by using
chemical bath deposition method
Parameters:
• NTA concentration
• Deposition time
• Deposition of multilayer CdSe
thin film
Characterization:
• XRD
• SEM
• UV-Vis
• EDX
Synthesis of polysulfide electrolyteFabrication of Cu2S
photocathode
Solar cell assembly Characterization
• Photo-electrochemical
Measurement (I-V)

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Methodology
Figure 3: Polysulfide electrolyte Figure 4: Brass counter electrode after immersed in
37% HCl at 70°C for 45 minutes
Figure 5: Cell assembly with polysulfide electrolyte
injected between the two electrodes

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Result and Discussion
(a) (b)
Figure 6: TiO2 thin films (a) before annealed and
(b) after annealed
TiO2
nanoparticle
Pore
Structure
Figure 7: FESEM image of TiO2 mesoporous layer at magnification
30.00KX
TiO2 Mesoporous Layer

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0
0.5
1
1.5
2
2.5
340 390 440
Absorbance(a.u)
Wavelength(nm)
0
5
10
15
20
25
30
35
40
3.2 3.3 3.4 3.5 3.6
(hv)2
optical band gap(eV)
Figure 8: Absorbance spectra of TiO2
mesoporous layer
Figure 9: (αhν)2 versus optical band
gap

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Figure 10: CdSe solution with 240, 180 and 120mM
NTA from left to right
240mM
NTA
180mM
NTA
120mM
NTA
CdSe Solution

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XRD Analysis of CdSe Nanoparticles
Figure 11: XRD pattern of CdSe at different NTA concentration
selenium oxide
Figure 12: XRD pattern of CdSe quantum dots
(Mahajan, et al., 2013)
S.Mahajan, Rani, M., Dubey, R. B. & Mahajan, J., 2013. Characteristics and Properties of CdSe Quantum Dots. International Journal of Latest Research in
Science and Technology, 2(1), pp. 457-459.

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Sample Matching
peaks (hkl)
2θ
(degree)
Spacing, d
(Å)
FWHM, β
(°)
Crystallite
size (nm)
120mM NTA
CdSe
111 24.27 3.66 0.620 13.00
180mM NTA
CdSe
111 25.87 3.44 0.889 8.56
240 mM NTA
CdSe
111 25.44 3.50 3.16 2.45
Table 1: Different parameters of different NTA concentration of CdSe
nanoparticles obtained from XRD
Scherrer’s Equation to
calculate crystallite
size,
D =
0.94λ
β cosθ

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FTIR Analysis of CdSe Nanoparticles
Figure 13: FTIR spectra of CdSe at different NTA concentration
H bond
(-OH group)
C-H bondingCOO- stretchingC-O group,
NTA exist
Cd(OH)2
Zhang, A. et al., 2012. Suppressed blinking behavior of CdSe/CdS QDs by polymer coating. Nanoscale, pp. 1-8.
Ingole, P. P. & Haram, S. K., 2010. Citrate-capped Quantum dots of CdSe for the Selective Photometric Detection of Silver Ions in Aqueous Solutions.
Liu, I.-S.et al., 2008. Enhancing photoluminescence quenching and photoelectric properties of CdSe quantum dots with hole accepting ligands. Journal of Materials Chemistry, Volume 18, pp. 675-682.
Corer, S. & Hodes, G., 1994. Quantum Size Effects in the Study of Chemical Solution Deposition Mechanisms of Semiconductor Films. J. Phys. Chem, Volume 98, pp. 5338-5346.
To determine the
existing of Cd(OH)2
because hydroxide
crystal from Cd(OH)2
in solution, act as
nuclei for formation of
CdSe (Corer & Hodes,
1994).

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UV-Vis of CdSe nanoparticles with different concentration of NTA
0.4
0.6
0.8
1
1.2
400 500 600 700
Absorbance
Wavelength(nm)
120mM NTA CdSe
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
400 500 600 700
Absorbance
Wavelength(nm)
180mM NTA CdSe
0.4
0.6
0.8
1
1.2
400 500 600 700
Absorbance
Wavelength(nm)
240mM NTA CdSe
Figure 14: a) Absorption spectra of CdSe at NTA concentration of 120mM, b) Absorption spectra of CdSe at NTA
concentration of 180mM, c) Absorption spectra of CdSe at NTA concentration of 240mM
(a) (b)
(c)

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Average diameter, D= (1.6122x10-9)λ4-(2.6575x10-6) λ3+(1.6242x10-3) λ2-(0.4277)
λ+41.57 (Peng, et al., 2003)
Sample 120mM NTA
CdSe
180mM NTA
CdSe
240mM NTA
CdSe
Wavelength
(nm)
608.94 554.98 587.48
Average
Diameter (nm)
5.00 3.14 4.09
Band gap
energy (eV)
1.93 2.10 1.95
Table 2: Wavelength, average diameter and band gap energy of CdSe
at different concentration
Yu, W. W., Qu, L., Guo, W. & Peng, X., 2003. Experimental Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals. Chemistry Material,
Volume 15, pp. 2854-2860.

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120mM
NTA
180mM
NTA
240mM
NTA
8 hr 14 hr 20 hr 26 hr
Figure 15: Deposited CdSe for 26 hours
on FTO glass with different NTA
concentration
Figure 16: Deposited CdSe with NTA
concentration of 240mM at different time
Deposition of CdSe on TiO2 Mesoporous Layer

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Time deposition (hr) 10.0KX 30.0KX
8
14
20
26
Figure 17:
FESEM image
of CdSe from
concentration of
180mM at
different time
under
magnification
of 10.0KX and
30.0KX

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NTA
concentration
(mM)
Time deposition
(hr)
Short Circuit
Current
Density, Jsc
(mA/cm2)
Open Circuit
Voltage, VOC
(V)
Fill factor, FF Efficiency, η
(%) (x 10-2)
8 0.055 0.145 0.323 2.6
120 14 0.095 0.085 0.366 3.0
20 0.465 0.091 0.283 12.0
26 0.905 0.182 0.286 47.1
8 0.212 0.184 0.388 15.1
180 14 0.350 0.217 0.281 21.3
20 0.127 0.160 0.336 6.8
26 0.105 0.123 0.283 3.7
8 0.967 0.227 0.316 69.4
14 0.509 0.195 0.326 32.4
240 20 0.550 0.131 0.244 17.6
26 0.448 0.131 0.331 19.4
Table 3: Summary of short
circuit current density, open
circuit voltage and
efficiency at
120mM,180mM and
240mM NTA concentration

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Deposition of CdSe Nanoparticles Multilayer on TiO2 Mesoporous Layer
Figure 18: CdSe multilayer deposited with 1st
layer is from 120mM NTA concentration at 26
hours and 2nd layer is from 180mM NTA
concentration at 14 hours
CdSe multilayer
FTO glass fracture
Figure 19: FESEM image of cross section
image of CdSe multilayer on FTO glass at
magnification of 1KX

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First Layer Second Layer
Short
Circuit
Current
Density, Jsc
(mA/cm2)
Open
Circuit
Voltage,
VOC (V)
Fill
factor,
FF
Efficiency,
η (%)
(x 10-2)
NTA
concentration
(mM)
Time
deposition
(hr)
NTA
concentration
(mM)
Time
deposition
(hr)
120 (b) 26 180 14 0.521 0.176 0.310 28.4
120 (b) 26 240 8 0.132 0.070 0.297 2.7
180 14 120 (b) 26 0.102 0.027 0.310 0.9
180 14 240 (b) 8 0.303 0.080 0.195 4.7
240 8 120 (b) 26 0.722 0.251 0.271 49.1
240 (b) 8 180 14 0.302 0.155 0.262 12.3
Table 4: Summary of short circuit current density, open circuit voltage and efficiency for deposited CdSe
multilayer at different NTA concentration and different time deposition
* (b) means bigger
average diameter
of particles

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Conclusion
• By changing NTA complex agent concentration with 120mM, 180mM and 240mM, different CdSe
nanoparticle size 5.00nm, 3.14nm and 4.09nm with band gap energy 1.93eV, 2.10eV and 1.95eV
had been synthesized respectively.
• For NTA concentration of 120mM, as time deposition increased, the efficiency also increased.
However, for NTA concentration of 180mM and 240mM, overall efficiency decreased as the time
deposition increase.
• Two layer of CdSe nanoparticles with different particle size had been deposited on FTO substrate
by CBD method.
• However, 2nd layer deposition of CdSe did not enhance the overall cell efficiency

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Recommendation
• Ostwald ripening process in the CdSe solution gives low conversion efficiency of the cells.
• The change in colour from yellow, orange and then finally red or dark red shown that CdSe
nanoparticles growing bigger.
• To avoid ostwald ripening, once the CdSe solution is synthesized, the substrate should be
deposited at once so that the CdSe nanoparticles can be deposited onto substrate and nucleation
takes place on the substrate before agglomeration occurs.
• Higher temperature deposition can be carried out too so that the CdSe nanoparticles gain energy
and will not agglomerate together.
• Besides that, when the CdSe solution is not used, the solution should always be stirred so that the
CdSe nanoparticles can be dispersed well and have a good particle distribution.

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Thank you!
Presented by
Sin Khai Wen 116541/ School of Materials & Mineral Resources
Engineering

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(a) (b)
(c)
Figure 20: (αhν)2 versus optical band gap of (a) CdSe at NTA concentration of 120mM, (b) CdSe at NTA concentration
of 180mM, (c) CdSe at NTA concentration of 240mM

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Figure 21: EDX data of CdSe from 180mM NTA
concentration deposited at 26 hours
Morphology of CdSe

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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Currentdensity,J(mA/cm2)
Voltage, V (v)
Figure 22: Graph of current density-voltage for deposited CdSe from NTA
concentration of 120mM
8h
14h
20h
26h

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0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.05 0.1 0.15 0.2 0.25
Voltage, V (v)
8h
14h
20h
26h

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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.05 0.1 0.15 0.2 0.25
Voltage, V (v)
8h
14h
20h
26h

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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.05 0.1 0.15 0.2 0.25 0.3
Voltage, V (v)
Figure 25: Graph of current density-voltage for deposited CdSe multilayer
from different NTA concentration and different time deposition
0.12mM 26h,0.18mM 14h
0.12mM 26h,0.24mM 8h
0.18mM 14h,0.12mM 26h
0.18mM 14h, 0.24mM 8h
0.24mM 8h,0.12mM 26h
0.24mM 8h,0.18mM 14h

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