Sin Khai Wen FYP Viva Presentation

W e l e a d

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

W e l e a d

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.

W e l e a d

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)

SeSO32- + OH- HSe- + SO4

2- (5)

The overall reaction can be described as follow

Cd(OH)2 (s) + HSe- CdSe + OH- + H2O (6)

,

W e l e a d

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.

W e l e a d

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

W e l e a d

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.

W e l e a d

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)

W e l e a d

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

W e l e a d

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

W e l e a d


0

0.5

1

1.5

2

2.5

340 390 440

Abso

rban

ce (

a.u)

Wavelength(nm)

0

5

10

15

20

25

30

35

40

3.2 3.3 3.4 3.5 3.6

(h

v)2

optical band gap(eV)

Figure 8: Absorbance spectra of TiO2

mesoporous layer

Figure 9: (αhν)2 versus optical band

gap

W e l e a d


Figure 10: CdSe solution with 240, 180 and 120mM

NTA from left to right

240mM

NTA

180mM

NTA

120mM

NTA

CdSe Solution

W e l e a d


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.

W e l e a d

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

W e l e a dResult and Discussion

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).

W e l e a d


UV-Vis of CdSe nanoparticles with different concentration of NTA

0.4

0.6

0.8

1

1.2

400 500 600 700

Ab

sorb

ance

Wavelength(nm)

120mM NTA CdSe

0.40.50.60.70.80.9

11.11.21.3

400 500 600 700

Ab

sorb

ance

Wavelength(nm)

180mM NTA CdSe

0.4

0.6

0.8

1

1.2

400 500 600 700

Ab

sorb

ance

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)

W e l e a d

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.

W e l e a d


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

W e l e a dResult and Discussion

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

W e l e a d


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

W e l e a d


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 glassfracture

Figure 19: FESEM image of cross section

image of CdSe multilayer on FTO glass at

magnification of 1KX

W e l e a d

First Layer Second LayerShort

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

Result and DiscussionTable 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

W e l e a d

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

W e l e a d

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.

W e l e a d

Thank you!

Presented by

Sin Khai Wen 116541/ School of Materials & Mineral Resources

Engineering

W e l e a d

Back up Slides

W e l e a d

(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


W e l e a d


Figure 21: EDX data of CdSe from 180mM NTA

concentration deposited at 26 hours

Morphology of CdSe

W e l e a d

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

Curr

ent

den

sity

, J

(mA

/cm

2)

Voltage, V (v)

Figure 22: Graph of current density-voltage for deposited CdSe from NTA

concentration of 120mM

8h

14h

20h

26h


W e l e a d


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

Curr

ent

den

sity

, J

(mA

/cm

2)

Voltage, V (v)



8h

14h

20h

26h

W e l e a d

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

Curr

ent

den

sity

, J

(mA

/cm

2)

Voltage, V (v)



8h

14h

20h

26h


W e l e a d

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

Curr

ent

den

sity

, J

(mA

/cm

2)

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


Sin Khai Wen FYP Viva Presentation

Documents

Transcript of Sin Khai Wen FYP Viva Presentation