Preparation and characterization of electrodeposited

Preparation and characterization of electrodeposited

Cu4SnS4 thin films

By

ASSOCIATE PROFESSOR DR HO SOONMIN

2017

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Title: Preparation and characterization of electrodeposited Cu4SnS4 thin films

Author : DR HO SOONMIN

Edition: First

Volume: I

© Copyright Reserved 2017

All rights reserved. No part of this publication may be reproduced, stored, in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, reordering or otherwise, without the prior permission of the publisher.

ISBN: 978-81-934005-0-0

Preparation and characterization of electrodeposited Cu4SnS4 thin films iii

Ideal International E-Publication Pvt. Ltd.

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Table of content

Pages

Chapter 1: Introduction 1-7

Chapter 2: Literature review 8-17

Chapter 3: Materials and Methods 18-25

Chapter 4: Cyclic voltammetry studies 27-33

Chapter 5: Electro deposition method 34-68

Preparation and characterization of electrodeposited Cu4SnS4 thin films 1


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CHAPTER 1: INTRODUCTION

Is this solar energy will appear to be one of the most promising ways to meet the

energy demands of the future? Is this the thin films solar cells can replace the silicon solar

cells in one day? The answer absolutely is yes. The availability of cheap sources of primary

energy is a reliable indicator of the standard of living in any country of the world. Worldwide

energy demand is predicted to keep growing with the world population and with the standard

of living that can be afforded. In today’s world, fossil and nuclear fuels are the world’s

primary energy sources. The global resources of fossil fuels are limited and their

consumption implies emission of the greenhouse gases like carbon dioxide, which is of major

concern since global warming seems to be emerging as a reality.

The solar cells are considered a major candidate for obtaining energy from the sun,

since it can convert sunlight directly to electricity. Recently, the use of photoelectrochemical

solar cells leads to a large amount of research on the search for metal chalcogenide thin films

[1-20] with acceptable efficiency. The binary, ternary and quaternary chalcogenides have

potential application in solar energy conversion. These materials to be potential candidates in

solar cells due to the band gap energy between 0.9 to 2.5 eV [21-36]. Thin films have been

prepared by various techniques such as chemical bath deposition, electrodeposition,

molecular beam epitaxy, close spaced sublimation, sputter deposition and metal organic

chemical vapor deposition. Among these techniques, electrodeposition and chemical bath

deposition method are more attractive since these methods offer the advantages of simple,

low-cost and convenient for large area deposition.

Up-to-date, the solar cells include both crystalline silicon solar cells and new thin-film

technologies such as cadmium telluride and copper indium gallium diselenide. The high

growth rate of thin film production and increase of the total production share indicate that the

thin film technology is gaining more and more acceptance. Currently, there are more than 130

companies which are involved in the thin film solar cells production process ranging from

research and development activities to major manufacturing plants. At present, the most

common material used in photovoltaic technology is silicon. The ongoing shortage in silicon

feedstock and the market entry of companies offering turn-key production lines for thin film

solar cells led to a massive expansion of investments into thin film capacities.



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1.1 Solar cells technology

The conversion of sunlight directly into electricity using the photovoltaic properties of

suitable materials is the most elegant energy conversion process. A laboratory curiosity for

more than a hundred years, solar cell technology has seen enormous development during the

last three decades, initially in providing electrical power for space craft, and satellite.

Furthermore, more recently for terrestrial systems such as aero plane, housing area, charger,

flash light, security camera, hand phone, watch, golf car, street light, calculator, radio and

boat.

1.2 History of solar cells

The photovoltaic effect was discovered by Alexandre-Edmond Becquerel in 1839.

This was the starting of the solar cell technology. Two electrodes were illuminated with

various types of light in his experiment. The electrodes were coated by light sensitive

materials such as AgCl and carried out in a black box surrounded by acid solution. He found

that the electricity increased when the light intensity was increased.

1.3 Crystalline silicon solar cells

In 1954, Gerald Pearson, Daryl Chapin and Calvin Fuller discovered a crystalline

silicon solar cell in Bell laboratories. This was the first material to directly convert sunlight

into electricity to run electrical devices. Initially, the efficiency of their material was 4%

which later successfully increased to 11%.

On the other hand, the scientists from RCA laboratories produced the first amorphous

silicon solar cells in 1976. This material was less expensive as compared with crystalline

silicon devices. However, the efficiency was only about 1 %. In 1985, the researchers from

University of South Wales successfully increased the efficiency of solar cells to 20%.

Currently, this type of solar cell has laboratory energy conversion efficiencies over 25 %.

1.4 Metal chalcogenide thin films

Thin film materials usually have high absorption coefficients so that most of the light

can be absorbed in a layer of about 1 m or less. The main advantage of thin films based

solar cell is their promise of lower costs, since less energy for processing and relatively lower



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costs for the materials are required and large scale production is feasible. Also, the metal

chalcogenide thin films should be low cost, non-toxic, robust and stable. The metal

chalogenides can produce either n-type or p-type semiconductor. Generally, p-type material

is preferred because electrons in many cases have a higher mobility and the materials

therefore exhibit a higher minority carrier length.

The CdTe thin films have been used in solar cells application since 1980. The

efficiency of solar cell made from CdTe is 15 % due to its direct bandgap at 1.5 eV at room

temperature. These films could be deposited on a substrate using electrodeposition, chemical

surface deposition and vapor transport deposition method. Currently, First Solar crushed the

conversion efficiency mark for CdTe with a world record 21.5%.

In 1980, the first cadmium sulphide thin film solar cells exceeds 10% efficiency was

produced in University of Delaware. But, cadmium is a highly toxic substance which can

accumulate in food chains. Therefore, many researchers are currently investigating cadmium-

free thin film solar cells such as copper indium gallium diselenide (CIGS). The best

efficiecny achieved 21.7 % as reported by Flisom in 2014.

1.5 Dye-sensitized solar cells

The dye-sensitized solar cell is a relatively new class of low cost photovoltaic cells as

reported by many researchers [37-40]. It is based on semiconductor produced between a

photo-sensitized anode and an electrolyte. The dye-sensitized solar cell is attractive due to it

is made of low-cost materials and does not require elaborate apparatus to manufacture. Its

manufacture could be significantly less expensive than older solid-state cell designs.

Nowadays, the efficiency of these type solar cells can be achieved more than 10%.

Basically, the titanium dioxide became the semiconductor of choice. The material has

many benefits such as low cost, widely available and non-toxic. The titanium dioxide covered

with a molecular dye that absorbs sunlight. In the photoelectrochemical system, the titanium

dioxide (anode) and platinum (cathode) were immersed under an electrolyte solution.

The sunlight passes via the transparent electrode into the dye layer then excite

electrons that flow into the titanium dioxide. The electrons flow toward the transparent

electrode where they are collected for powering a load. After flowing through the external

circuit, they are re-introduced into the cell on a metal electrode on the back, flowing into the

electrolyte. The electrolyte then transports the electrons back to the dye molecules. The dye



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molecules are quite small, in order to capture sunlight, the layer of dye molecules needs to be

made fairly thick, normally, much thicker than the molecules themselves.

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10. Saravanan, N., Anuar, K., Ho, S.M., Abdul, H.A., & Noraini, K. (2010). Influence of

the deposition time on the structure and morphology of the ZnS thin films

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Influence of sodium incorporation on kesterite Cu2ZnSnS4 solar cells fabricated on

stainless steel substrates. Solar Energy Materials and Solar Cells, 157, 565-571.

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chemically deposited tin sulfide films. Universal Journal of Chemistry, 1, 170-174.

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19. Ho, S.M., Anuar, K., Loh, Y.Y., & Saravanan, N. (2010). Structural and

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20. Shaji, S., Garcia, L.V., Loredo, S.L., Krishnan, B., Martinez, J.A., Roy, T.K., &

Avellaneda, D.A. (2017). Antimony sulfide thin films prepared by laser assisted

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21. Ho, S.M., Saravanan, N., Anuar, K., & Tan, W.T. (2012). Temperature dependent

surface topography analysis of SnSe thin films using atomic force microscopy. Asian

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22. Ho, S.M. (2014). Atomic force microscopy investigation of the surface morphology

of Ni3Pb2S2 thin films. European Journal of Scientific Research, 125, 475-480.

23. Mobarak, M., & Shaban, H.T. (2014). Characterization of CuInTe2 crystals. Materials

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24. Roy, S., Bhattacharjee, B., Kundu, S.N., Chaudhuri, S., & Pal, A.K. (2003).

Characterization of CuInTe2 thin film synthesized by three source co-evaporation

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25. Ananthan, M.R., & Kasiviswanathan, S. (2009). Growth and characterization of

stepwise flash evaporated CuInTe2 thin films. Solar Energy Materials and Solar

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26. Kazmerski, L.L., & Juang, Y.J. (1998). Vacuum deposited CuInTe2 thin films:

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27. Boustani, M., Assali, K.E., Bekkay, T., & Khiara, A. (1997). Structural and optical

properties of CuInTe2 films prepared by thermal vacuum evaporation from a single

source. Solar Energy Materials and Solar Cells, 45, 369-376.

28. Manorama, L., Mahapatra, S.K., & Chaure, N.B. (2016). Development of CuInTe2

thin film solar cells by electrochemical route with low temperature (80 °C) heat

treatment procedure. Materials Science and Engineering B, 204, 20-26.

29. Lakhe, M., & Chaure, N.B. (2014). Characterization of electrochemically deposited

CuInTe2 thin films for solar cell applications. Solar Energy Materials & Solar Cells,

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30. Dixit, P., Kavita, D., Ashok, K.S., Vikas, T., & Poolla, R. (2013). Electrochemical

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31. Cham, K., Dong, H.K., Young, S.S., Kim, H., Jea, Y.B., & Yoon, S.H. (2012).

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32. Tembhurkar, Y.D. (2016). Annealing effect on structural and electrical properties of

CuInTe2 thin films. International Journal of Scientific Research, 5, 504-506.

33. Prabukanthan, P., Asokan, K., Avasthi, D.K., & Dhanasekaran, R. (2007). Effect of

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CHAPTER 2: LITERATURE REVIEW

There are many review articles [1-26] and research articles related to preparation of

thin films. Generally, deposition techniques could be categorized into two groups, namely

physical method and chemical deposition technique. These deposition methods have been

employed by many researchers from around the world to synthesize binary, ternary and

quaternary thin films.

2.1 Thin film deposition methods

Thin film deposition is any method for depositing a thin film of material onto

substrates. There are two categories of thin film processes, namely chemical and physical

process. The example of chemical process such as chemical vapor deposition, chemical bath

deposition and electrodeposition while physical process like sputter deposition, vacuum

evaporation and pulsed laser deposition. The advantages and disadvantages of techniques

have been briefly summarized in Table 1. From such a table, it is not possible to point out the

best way of preparing a thin film. The method used must depend on the type of film required

and the limitation present on choice of substrates. The costs of deposition technique also play

an important role in determining the mass output of thin film products in market.

Table 1 The advantages and disadvantages of different deposition techniques

Chemical vapor deposition [27-29]

Advantages High growth rates possible

Can deposit materials which are hard to evaporate

Can grow epitaxial films

Disadvantages High temperature

Complex processes

Toxic and corrosive gasses

Chemical bath deposition [30-58]

Advantages Low cost

Unnecessary conductive substrate

Low elaboration temperature

Simple instrumentation

Easy coating of large surface



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Disadvantages Deposition lasts for very long time

Electrodeposition [59-63]

Advantages Simple and economical method

Large area deposition

Low temperature growth

Easy to monitor

Control film thickness, morphology by adjusting electrical parameters

Disadvantages The films must be prepared on conducting substrates

Sputtering [64-66]

Advantages Adhesion can be very strong due to high energy particles forcing into substrates

The source and substrates can be spaced close together

There is very little radiant heat in the deposition process

The sputtering target provides a stable, long-lived

vaporization source

Disadvantages Suitable target required

Vacuum required

Use a plasma

High capital expenses are required

Most of the energy incident on the target becomes heat.

Vacuum evaporation [67-69]

Advantages Deposition rate monitoring and control are relatively easy

High purity films, thicker layers with better crystallinity and

stoichiometry are produced

Disadvantages Vacuum apparatus required

Some materials decompose on heating

Poor surface coverage

Pulsed laser deposition [70-73]

Advantages High quality samples can be grown reliably in 10 minutes

One laser can serve many vacuum systems

The laser beam vaporizes a target surface, producing a film

with the same composition as the target

Disadvantages Debris generation and coating flux falling off rapidly with

distance from the source

Difficulty to controlling thickness uniformly across the samples



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2.2 Electrodeposition method

Electrodeposition is a cost effective method of depositing thin films. It is also usually

a convenient method since all the elements deposited in a single step. There is no need for a

vacuum system and the process can be scaled very easily to any substrate size. Often, the

composition of the deposited material can be controlled through one or more of the

deposition parameters. However, the electrodeposition of ternary compounds is more

complex as they involve several deposition parameters which control the film properties such

as film structure and morphology. This is due to the possibility of the formation of

intermediate phases during electrodeposition.

2.3 Chemical bath deposition method

The chemical bath deposition is a low cost technique for the large area deposition of

thin film. The other advantages of this technique are simple and deposition at low

temperature. In most of the experimental approaches, substrates are immersed in an aqueous

solution (alkaline or acidic solution) containing the chalcogenide source, metal ion and

complexing agents. In chemical bath deposition, a complexing agent is used to bind the

metallic ions to avoid the homogeneous precipitation of the corresponding compound. The

formation of a complex ion is essential to control the rate of the reaction and to avoid the

immediate precipitation of compound in the solution. When the solution is saturated, the

ionic product is equal to solubility product. As the ionic product slowly exceeds the solubility

product the solution becomes supersaturated and precipitation occurs. The deposition begins

with nucleation phase followed by growth phase in which the thickness of film increases with

time.

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value and electrolyte concentration on the copper sulphide thin films prepared by

chemical bath deposition method. Gazi University Journal of Science, 23, 435-443.

37. Cortes, A., Gomez, H., Marotti, R.E., Riveros, G., & Dalchiele, E.A. (2004). Grain

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38. Anuar, K., Saravanan, N., Tan, W.T., Ho, S.M., & Teo, D. (2010). Chemical bath

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39. Ezema, F.I., & Osuji, R.U. (2007). Band gap shift and optical characterization of

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40. Anuar, K., Tan, W.T., Ho, S.M., Shanthi, M., & Saravanan, N. (2010). Effect of bath

temperature on the chemical bath deposition of PbSe thin films. Kathmandu

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41. Ezema, F.I., & Osuji, R.U. (2007). Preparation and optical properties of chemical bath

deposited MnCdS2 thin films. FIZIKA A (Zagreb), 16, 107-116.

42. Gaewdang, N., & Gaewdang, T. (2005). Investigations on chemically deposited Cd1-

xZnxS thin films with low Zn content. Materials Letters, 59, 3577-3584.

43. Anuar, K., Ho, S.M., Loh, Y.Y., & Saravanan, N. (2010). Structural and

morphological characterization of chemical bath deposition of FeS thin films in the

presence of sodium tartrate as a complexing agent. Silpakorn University Science and

Technology Journal, 4, 36-42.

44. Khefacha, Z., Benzarti, Z., Mnari, M., & Dachraoui, M. (2004). Electrical and optical

properties of Cd1-xZnxS (0x0.18) grown by chemical bath deposition. Journal of

Crystal Growth, 260, 400-409.

45. Gumus, C., Ulutas, C., & Ufuktepe, Y. (2007). Optical and structural properties of

manganese sulfide thin films. Optical Materials, 29, 1183-1187.

46. Anuar, K., Tan, W.T., Jelas, M., Ho, S.M., & Gwee, S.Y. (2010). Effects of

deposition period on the properties of FeS2 thin films by chemical bath deposition

method. Thammasat International Journal of Science and Technology, 15, 62-69.

47. Hankare, P.P., Chate, P.A., Asabe, M.R., Delekar, S.D., Mulla, I.S., & Garagkar,

K.M. (2006). Characterization of Cd1-xZnxSe thin films deposited at low temperature

by chemical route. Journal of Materials Science: Materials in Electronics, 17, 1055-

1063.

48. Anuar, K., Ho, S.M., Tan, W.T., & Ngai, C.F. (2011). Influence of triethanolamine on

the chemical bath deposited NiS thin films. American Journal of Applied Sciences, 8,

359-361.

49. Mane, R.S., & Lokhande, C.D. (2002). Photoelectrochemical cells based on

nanocrystalline Sb2S3 thin films. Materials Chemistry and Physics, 78, 385-392.

50. Mane, R.S., Sankapal, B.R., Gadave, K.M., & Lokhande, C.D. (1999). Preparation of

CdCr2S4 and HgCr2S4 thin films by chemical bath deposition. Materials Research

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51. Anuar, K., Abdul, H.A., Ho, S.M., & Saravanan, N. (2010). Effect of deposition time

on surface topography of chemical bath deposited PbSe thin films observed by atomic

force microscopy. Pacific Journal of Science and Technology, 11, 399-403.

52. Mane, R.S., Todkar, V.V., & Lokhande, C.D. (2004). Low temperature synthesis of

nanocrystalline As2S3 thin films using novel chemical bath deposition route. Applied

Surface Science, 227, 48-55.

53. Anuar, K., Tan, W.T., Ho, S.M., Abdul, H.A., Ahmad, H.J., & Saravanan, N. (2010).

Effect of solution concentration on MnS2 thin films deposited in a chemical bath.

Kasetsart Journal: Natural Science, 44, 446-453.

54. Prabahar, S., & Dhanam, M. (2005). CdS thin films from two different chemical

baths-structural and optical analysis. Journal of Crystal Growth, 285, 41-48.

55. Seghaier, S., Kamoun, N., Brini, R., & Amara, A.B. (2006). Structural and optical

properties of PbS thin films deposited by chemical bath deposition. Materials


56. Sonawane, P.S., Wani, P.A., Patil, L.A., & Seth, T. (2004). Growth of CuBiS2 thin

films by chemical bath deposition technique from and acidic bath. Materials


57. Ubale, A.U., Sangawar, V.S., & Kulkarni, D.K. (2007). Size dependent optical

characteristics of chemically deposited nanostructured ZnS thin films. Bulletin

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58. Soundeswaran, S., Kumar, O.S., & Dhanasekaran, R. (2004). Effects of ammonium

sulphate on chemical bath deposition of CdS thin films. Materials Letters, 58, 2381-

2385.

59. Salim, H.I., Olusola, O.I., Ojo, A.A., Urasov, K.A., Dergacheva, M.B., &

Dharmadasa, I. (2016). Electrodeposition and characterization of CdS thin films using

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60. Anuar, K., Ho, S.M., Abdul, H.A., Noraini, K., & Saravanan, (2010). Influence of the

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61. Henriquez, R., Vasquez, C., Briones, N., Munoz, E., Leyton, P., & Dalchiele, E.A.

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and hydrothermal low temperature techniques. International Journal of

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63. Echendu, O.K., Okeoma, K.B., Oriaku, C.I., & Dharmadasa, I.M. (2016).

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frequency magnetron sputtering: a versatile tool for CdSe quantum dots depositions

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66. Montes, J.I., Morales, A., Bernal, R., & Pulzara, A. (2016). Characterization of

CuInSe2 thin films obtained by RF magnetron Co-sputtering from CuSe and In

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69. Kathirvel, D., & Jeyachitra, R. (2016). Structural properties of vacuum evaporated

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71. Sun, L., He, J., Kong, H., Yue, F., Yang, P., & Chu, J. (2011). Structure, composition

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Films, 423, 273-276.



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CHAPTER 3: MATERIALS AND METHODS

3.1 Chemicals used

All the chemicals used for the deposition were analytical grade without further

purification. The chemicals include copper sulfate (CuSO4, Ajax Chemical), tin chloride

(SnCl2, Merck), sodium thiosulfate (Na2S2O3.5H2O, Hamburg Chemical GmbH), potassium

hexacyanidoferrate (II) (K4[Fe(CN)6], BDH), Potassium hexacyanoferrate (III) (K3[Fe(CN)6],

BDH), sodium hydroxide (NaOH, Merck), ethanol (C2H5OH) and hydrochloric acid (HCl).

All the solutions were prepared using deionised water from Millipore Alpha-Q System.

3.2 Electrodeposition method

3.2.1 Electrochemical cells

Electrodeposition was carried out in a 100 mL electrochemical cell consisting of a three-

electrode system (Figure 3.1). The working electrode was indium tin oxide (ITO) coated

glass substrate while counter electrode was a platinum wire. A silver-silver chloride electrode

(Ag/AgCl) was used as a reference electrode and all potentials are given versus Ag/AgCl.

The reference electrode was placed as close as possible to the working electrode and counter

electrode as well. This is due to minimize cell resistance and maximize current flow between

counter electrode and working electrode. The cell is five-hole PVC covered attached directly

to a retort stand to accommodate a pH electrode, nitrogen gas tube, working electrode,

counter electrode and reference electrode.

Figure 3.1 The electrodeposition method set-up



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3.2.2 Working electrode

The indium tin oxide coated glass substrates were used as a working electrode. The

ITO glass substrates were first cleaned in ethanol solution for 10 minutes to remove dirty and

oily substance from the surface. Then, it was cleaned with distilled water for 15 minutes in an

ultrasonic cleaner. Finally, it dried in desiccator prior to deposition. In this study, the ITO

glass obtained from the manufacturer (Samsung Corporation). The ITO glass was cut into

desired dimension (1cm x 2 cm) using a glass cutter.

3.2.3 Reference electrode

The silver-silver chloride electrode (Ag/AgCl) was chosen as the reference electrode

due to easily and cheaply prepared. It is also stable and quite robust. Its potential is 0.222 V

against standard hydrogen electrode. The Ag/AgCl reference electrodes are easily ruined by

drying. Keep the tips wetted at all times and store in 3 M NaCl when not in use.

3.2.4 Counter electrode

The platinum wire was used as the counter electrode during deposition. The surface

was polished with alumina slurry.

3.3 Cyclic voltammetry

Prior to the deposition process, cyclic voltammetry was used to monitor the

electrochemical reactions in solutions of CuSO4, SnCl2, Na2S2O3 and mixtures, in order to

find the suitable deposition potential range. All voltammetry curves were scanned first in the

cathodic direction and the positive current density indicates a cathodic current. Cyclic

voltammograms were carried out at a sweep rate of 10 mV/s using Bioanalytical System.

3.4 Electrodeposition process

Copper tin sulfide electrodeposition was carried out in an electrochemical cell

consisting of a three-electrode system under a potentiostatic mode. Aqueous solutions of

CuSO4, SnCl2 and Na2S2O3 were used as Cu2+, Sn2+ and S2- source, respectively. The nitrogen

gas was flowed into the solutions prior to mixing to remove any dissolved oxygen. The

deposition was carried out in an unstirred bath by varying deposition parameters such as



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deposition potential, deposition time, deposition temperature, solutions concentration and

solution pH. After completed deposition, the films were rinsed with distilled water and were

used for further characterizations.

3.4.1 Investigation of different deposition potentials

The thin films were deposited from the solutions consisted of 20 mL of 0.01 M

CuSO4, 0.01 M SnCl2 and 0.01 M Na2S2O3. The pH was adjusted to pH 1.5 with hydrochloric

acid using pH meter. The deposition process was carried out for 45 min at 25 C. Based on

the cyclic voltammetry studies, the deposition process was done under various potentials

from -400 mV to -1000 mV versus Ag/AgCl.

3.4.2 Investigation of different deposition temperatures

In this experiment, the deposition process was done at a deposition potential of -600

mV versus Ag/AgCl under various bath temperatures from 25 to 50 C while other deposition

conditions were unchanged.

3.4.3 Investigation of different solutions concentration

In order to investigate the effect of electrolytes concentration on the thin film

properties, deposition at various concentrations was carried out. The first set of experiment

was carried out using constant concentration of 0.01 M of CuSO4, SnCl2 and varying

concentrations of Na2S2O3 (0.01 M – 0.02 M) solutions. The second set of experiment was

carried out using fixed concentration of 0.01 M of CuSO4, Na2S2O3 and varying

concentrations of SnCl2 (0.01 M – 0.02 M) solutions. The third set of experiment was carried

out using constant concentration of 0.01 M of SnCl2, Na2S2O3 and varying concentrations of

CuSO4 (0.01 M – 0.02 M) solutions.

3.4.4 Investigation of different deposition periods

In this experiment, the deposition process was done under various deposition periods

from 15 to 60 minutes while other conditions were unchanged.



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3.4.5 Investigation of different pH values

In this experiment, the deposition process was done under various pH values from 1.1

to 2.0. The pH was adjusted to desired value with hydrochloric acid using pH meter.

3.5 Characterization methods

There are several characterization tools were used in order to investigate the general

properties of thin films [1-32]. Material characterization on a nano or mirco scale is often an

essential part for understanding material behavior. Obviously, no one technique can ever

solve each surface problem. Therefore, two or more techniques were used by material

scientists in their investigation.

3.5.1 X-ray Diffraction (XRD)

The crystalline structure of thin films was examined using X-ray diffraction. The

position and the intensities of the peaks are used for identifying the underlying structure of

the materials. The patterns obtained from experimental samples were compared to Joint

Committee on Powder Data Standards (JCPDS) data to identify crystalline phases. A

SCINTAG XRD 2000 X-ray diffractometers using CuKα (λ=1.5418 Å) was used for this

study. The scanning rate was set to 2/min with a 0.02 step size and the range from 20 to

60. The relationship describing the angle at which a beam of X-rays of a particular

wavelength diffracts from a crystalline surface is known as Bragg’s Law.

..........(1)

= wavelength of the X-ray

= diffraction angle

n= integer representing the order of diffraction peak

d = interplanar spacing generating the diffraction

3.5.2 Atomic Force Microscopy (AFM)

The atomic force microscopy (AFM) was performed on the sample to analyze the

surface morphology of thin films from angstroms (Å) to 100 m. In this study, AFM was

carried out using a Q–Scope 250 (Quesant Instrument Corporation) which operating in



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contact mode with a commercial Si3N4 cantilever. It is the most popular Quesant model,

primarily used in stand-alone applications. It is equipped with PC-based video subsystem

using a CCD camera for 90° tip and sample viewing and a manual X-Y translation stage for

sample positioning. It also provides a three-dimensional surface profiles.

3.5.3 UV-Visible Spectrophotometer

Ultraviolet Visible spectroscopy involves the spectroscopy of the photons and

spectrophotometry. It uses light in the visible and ultraviolet region. In this region of energy

space molecules undergo electronic transitions. In this study, Perkin Elmer UV-Vis

Spectrophotometer Lambda 20 has been used for investigation of the absorption spectra of

the samples. The indium tin oxide coated glass substrate was placed in the reference path

while the deposited films in the sample radiation path. The optical properties of films

deposited on ITO glass substrates were investigated from the absorption measurements in the

range of 300-800 nm. The band gap energy and transition type were derived from

mathematical treatment with the following relationship for near-edge absorption

..........(2)

Where A is absorbance, Eg is band gap energy, h is Plank’s constant (6.63x10-34), v is

frequency in Hertz, k equals a constant value, n carries the value of either 1 or 4. The

arrangement of the equation (1) gives the following equation:

..........(3)

For a direct transition when n=1, the equation (2) becomes

..........(4)

For an indirect transition when n=4, the equation (2) becomes

..........(5)



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The data were used to plot a graph of (Ahv)2/n versus hv. Extrapolation of the line to the base

line, where the value of (Ahv)2/n is zero, will give band gap energy.

3.5.4 Photoelectrochemical test (PEC)

The photoactivity of the samples were test in 0.01 M [Fe(CN)6]3-/[Fe(CN)6]4- redox

system by running linear sweep voltammetry technique (LSV) between two potentials limits

(-1000 mV to 1000 mV versus Ag/AgCl). The BAS Potentiostat was used to control the

process and to monitor the current and voltage profiles. The system consists of deposited film

as a working electrode, platinum wire as counter electrode and Ag/AgCl as reference

electrode. The photocurrent (Ip) and darkcurrent (Id) of the PEC cells were recorded under

light illumination and dark condition. The halogen lamp (300W) was used for illuminating

the electrode. The light path towards the PEC cells was chopped manually to study the effect

on photoactivity behavior.

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5. Ho, S.M., Saravanan, N., Anuar, K., & Tan, W.T. (2012). Temperature dependent

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CHAPTER 4: CYCLIC VOLTAMMETRY STUDIES

4.1 Cyclic voltammetry process

Cyclic voltammetry (CV) is a versatile electroanalytical technique for the study of

electroactive species in a standard electrochemical bath as reported by many researchers [1-

17]. The common characteristic of voltammetric technique is that they involve the application

of a potential (E) to an electrode and the monitoring of the resulting current (i) flowing

through the electrochemical cell.

Cyclic voltammetry is widely used for the study of redox processes, for understanding

reaction mechanisms and for obtaining stability of reaction products. This technique is based

on varying the applied potential at a working electrode in both forward and reverse directions

while monitoring the current. For example, the initial scan could be in the negative direction

to the switching potential. At that point the scan would be reversed and run in the positive

direction. Depending on the analysis, one full cycle, a partial cycle or a series of cycles can

be performed.

The important parameters in a cyclic voltammogram are the peak potentials (Epc, Ep

a)

and peak currents (ipc, ip

a) of the cathodic and anodic peaks, respectively (Figure 4.1). If the

electron transfer process is fast compared with other processes, the reaction is said to be

electrochemically reversible and the peak separation is

[Equation 1] Reversible couples will display a ratio of the peak currents passed at reduction (ipc)

and oxidation (ipa) that is near unity.

Figure 4.1 The typical cyclic voltammogram recorded for reversible single

electrode transfer reaction

http://en.wikipedia.org/wiki/File:Cyclovoltammogram.jpg



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For slow electron transfers at the electrode surface, i.e. irreversible processes, the

difference of peak potentials widen. The peak current in reversible systems for the forward

scan is given by Randles-Sevcik equation,

[Equation 2]

where, ip = peak current, n = number of electrons involved, A = electrode area, cm2; D

= diffusion coefficient, cm2/s; C = concentration, mol/cm3 and v = scan rate, V/s. Thus ip

increases with square root of v and is directly proportional to concentration of the species.

The basic components of a modern electroanalytical system for voltammetry are a

potentiostat, computer and the electrochemical cell. The task of applying a known potential

and monitoring the current falls to the potentiostat. Accurate and flexible control of the

applied potential is a critical function of the potentiostat.

4.2 Electrodeposition of copper tin sulphide thin films

The cyclic voltammogram was scanned in the potential range 1000 mV to –1000 mV

versus Ag/AgCl at a sweep rate 10 mVs-1. All voltammetry curves were scanned first in the

cathodic direction and positive current indicated a cathodic current.

In copper sulfate solution (Figure 4.2a), the current rise started at –50 mV, followed

by large reduction wave at –500 mV. This response was associated with Cu (II) reduction on

ITO substrate. The two stripping peaks at positive potential limits, 200-600 mV indicated the

oxidation of the copper compound.

Figure 4.2b shows the voltammogram recorded for tin chloride on ITO glass

substrate. The forward scan showed a reduction potential starting at about –500 mV.

Reduction peak increased towards the more-negative region where hydrogen evolution also

occurred. During the reverse scan, the oxidation wave of tin could be seen starting at about –

450 mV. This peak reached a maximum value of about –200 mV. The forward scan of

sodium thiosulfate solution (Figure 4.2c) shows the cathodic current to start flowing at about

–500mV. The shoulder at –700 mV might be associated with the reduction of thiosulphate

ions.



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(a)

(b)



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Figure 4.2 Cyclic voltammogram of (a) 0.01 M copper sulfate (b) 0.01M tin chloride (c) 0.01

M sodium thiosulfate (d) mixture of (a), (b) and (c) solutions at

(c)

(d)



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room temperature, scan rate: 10 mV/s and pH 1.5

Figure 4.2d shows the cyclic voltammogram of the ITO working electrode in the

mixture of copper sulfate, tin chloride and sodium thiosulfate. The wave around –475 mV

corresponded to the formation of Cu4SnS4 layers and the cathodic current increased gradually

up to –1000 mV, indicating the growth of layers. The anodic peak start from -500 mV

corresponded to the stripping of deposited layers in the reverse scan.

Figure 4.3 The cyclic voltammograms of electrodeposited Cu4SnS4 thin films on ITO substrate. The deposition bath contains CuSO4, SnCl2 and Na2S2O3 at

same concentration 0.01 M respectively at 25°C. Scan rate = 1, 10, 20, 60,100 mV/s in pH=1.5

Irreversibility reaction is when the rate of electron transfer is sufficiently slow, so that

the potential no longer reflects the equilibrium activity of redox couple at the electrode

surface. In such a case, the potential peak values will change as a function of the scan rate.



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The reduction peak at low scan rates (1 mV/s) is well marked. At high scan rates (which more

than 10mV/s), it widened and increased both in terms of peak currents and peak potentials.

When the scan rate increased, the peak separation also increased (Figure 4.3) due to the

heterogeneous kinetics and IR drop effects. The ohmic polarization effect is a

characterization of bulk solution. This effect can be minimized by proper cell design during

the experiment.

References

1. Jana, S., Mondal, P., TRipathi, S., Mondal, A., & Chakraborty, B. (2015).

Electrochemical synthesis of FeS2 thin film: An effective material for peroxide

sensing and terephthalic acid degradation. Journal of Alloys and Compounds, 646,

893-899.

2. Thanikaikarasan, S., Mahalingam, T., Sundaram, K., Kathalingam, A., Kim, Y., &

Kim, T. (2009). Growth and characterization of electro synthesized iron selenide thin

films. Vacuum, 83, 1066-1072.

3. Xue, M., & Fu, Z. (2007) Electrochemical properties of FeSe thin film electrode

fabricated by pulsed laser deposition. Acta Chimca Sinica, 65, 2715-2719.

4. Lai, Y., Liu, F., Zhang, Z., Liu, J., Li, Y., Kuang, S., Li, J., & Liu, Y. (2009). Cyclic

voltammetry study of electrodeposition of Cu(In, Ga)Se2 thin films. Electrochimica

Acta, 54, 3004-3010.

5. Lee, H., Lee, J., Hang, Y., & Kim, Y. (2014). Cyclic voltammetry study of

electrodeposition of CuGaSe2 thin films on ITO glass substrates. Current Applied

Physics, 14, 18-22.

6. Liu, J., Liu, F., Lai, Y., Zhang, Z., Li, J., & Liu, Y. (2011) Effects of sodium

sulfamate on electrodeposition of Cu(In,Ga)Se2 thin film. Journal of Electroanalytical

Chemistry, 651, 191-196.

7. Hsieh, M., Chen, C., & Whang, T. (2016). Triethanolamine facilitated one step electro

deposition of CuAlSe2 thin films and the mechanistic studies utilizing cyclic

voltammetry. Journal of Electroanalytical Chemistry, 762, 73-79.

8. Shin, S., Park, C., Kim, C., Kim, Y., Park, S., & Lee, J. (2016). Cyclic voltammetry

studies of copper, tin and zinc electro deposition in a citrate complex system for

CZTS solar cell application. Current Applied Physics, 16, 207-210.



www.isca.co.in

9. Kwinten, C., Koen, B., Edward, M., & Jan, F. (2016). Electrochemical studies of the

electrodeposition of copper zinc tin alloys from pyrophosphate electrolytes followed

by selenization for CZTSe photovoltaic cells. Electrochimica Acta, 188, 344-345.

10. Murilo, F.C., Dyovani, C., & Sergio, A.S. (2013). Analyzing Cd under potential

deposition behavior on Se thin films: Atomic force microscopy, cyclic voltammetry

and electrochemical quartz crystal nanobalance studies. Electrochimica Acta, 91, 361-

366.

11. Patil, S.J., Lokhande, V.C., Chodankar, N.R., & Lokhande, C.D. (2016). Chemically

prepared La2Se3 nanocubes thin film for super capacitor application. Journal of

Colloid and Interface Science, 469, 318-324.

12. Riahi, M., Martinez, C., Agouram, S., Boukhachem, A., & Maghraoui, H. (2017). The

effects of thermal treatment on structural, morphological and optical properties of

electrochemically deposited Bi2S3 thin films. Thin Solid Films, 626, 9-16.

13. Rohom, A.B., Londhe, P.U., & Chaure, N.B. (2016). Agitation dependent properties

of copper indium diselenide thin films prepared by electrochemical route. Thin Solid

Films, 615, 366-373.

14. Patil, A.M., Kumbhar, V.S., Chodankar, N.R., Lokhande, A.C., & Lokhande, C.D.

(2016). Electrochemical behavior of chemically synthesized selenium thin film.

Journal of Colloid and Interface Science, 469, 257-262.

15. Fernandez, A.M., Turner, J.A., Lara., B., & Deutsch, T.G. (2017). Influence of

support electrolytic in the electro deposition of Cu-Ga-Se thin films. Superlattices and

Microstructures, 101, 373-383.

16. Pujari, R.B., Lokhande, A.C., Shelke, A.R., Kim, J.H., & Lokhande, C. D. (2017).

Chemically deposited nano grain composed MoS2 thin films for super capacitor

application. Journal of Colloid and Interface Science, 496, 1-7.

17. Aghassi, A., Jafarian, M., Danaee, I., Gobal, F., & Mahjani, M.G. (2011). AC

impedance and cyclic voltammetry studies on PbS semiconducting film prepared by

electro deposition. Journal of Electroanalytical Chemistry, 661, 265-269.



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CHAPTER 5: ELECTRO DEPOSITION METHOD

5.1 Effect of deposition potential on the properties of films

Based on the cyclic voltammetry studies, the voltammogram suggested that a

deposition on the working electrode can be expected when the potential is -400 mV and

above (more negative values). Thus, the deposition process was carried out at various

deposition potentials from -400 mV to -1000 mV versus Ag/AgCl. The deposition was

carried out for 45 min at 25 C under acidic medium (pH 1.5) using 0.01 M of solutions

concentration.

Figure 5.1 X-ray diffraction pattern of samples prepared at different deposition potentials ( Cu4SnS4)

Figure 5.1 shows the XRD patterns for the films deposited at various deposition

potentials ranging from –400 mV to –1000 mV versus Ag/AgCl. Four main peaks at 2

=30.3, 35.5, 45.2 and 50.6, corresponding to d-spacing values 2.95, 2.55, 2.00 and 1.80 Å



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which attributed to the (221), (420), (512) and (711) planes, respectively were detected from

all the samples. All these peaks are related to the orthorhombic structure of Cu4SnS4 (a

=13.5580 Å, b = 7.6810 Å, c = 6.4120Å, α = β = γ =90°). The prominent peak corresponds to

(221) plane with the d-spacing value of 2.95Å can be seen. The XRD data shows that the

disappearance of the plane (312) as deposition potential was increased to –600mV and more

negative of values.

Atomic force microscopy (AFM) was used to study the topography of films. The

surface images in an area of 10 μm X 10 μm of the thin films deposited at various deposition

potential values are shown in Figure 5.2. It can be observed that the surface of the films was

not very compact (Figure 5.2a). The films were constituted by nano particles with an irregular

size distribution. A lot of empty spaces could be seen between these particles. AFM images

of samples clearly show the conversion of nano particles into spherical grains that were quite

uniform over the entire glass substrate (Figure 5.2c). However, it is seen from the intensity

distribution that the film consisted of smaller and larger nano particles in deposition potential

above –700 mV (Figure 5.2d to 5.2g). This might be due to the difference of rate of

nucleation and growth.

(a)



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(b)

(c)



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(d)

(e)



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Figure 5.2 Atomic force microscopy images of Cu4SnS4 thin films at different deposition potentials (versus Ag/AgCl). (a) –400 mV (b) –500 mV (c) –600 mV (d) –700 mV

(e) –800 mV (f) –900 mv (g) –1000 mV

(f)

(g)



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Deposition was carried out on an ITO glass substrate to study the optical behavior of

the Cu4SnS4 films in the range of 300 to 800 nm. Figure 5.3 shows the spectra gradually

increasing absorbance throughout the visible region for all samples, which makes it possible

for this material to be used in a photoelectrochemical cells. The absorbance of thin films

deposited at –600 mV produced higher absorbance value. However, it is seen from figure that

as the deposition potential increased (above –700 mV), the absorbance value decreased.

Figure 5.3 Absorbance versus wavelength spectra for Cu4SnS4 films deposited at different deposition potentials (versus Ag/AgCl)

5.2 Effect of deposition temperature on the properties of films

In order to study the effect of temperature on the properties of thin films, the films

prepared under various bath temperatures (25 C to 50 C). Other deposition parameters were

maintained as stated earlier.

Figure 5.4 shows the X-ray diffraction patterns for the films deposited at various bath

temperatures. The XRD patterns are found to be polycrystalline with orthorhombic structure.



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There are six peaks at 2=30.2°, 35.4.°, 42.9°, 47.4°, 50.7° and 57.5 °C were detected for

films deposited from 25 °C to 35 °C. The corresponding interplanar distances are well in

agreement with JCPDS data (Reference code: 010710129) of 0.296, 0.255, 0.210, 0.192,

0.180 and 0.161 nm which attributed to the (221), (420), (331), (040), (711) and (532) planes,

respectively. However, raising the bath temperature further to 40 °C and above, resulted in

the disappearance of (532) plane could be observed in XRD patterns. The most prominent

peak obtained at 2 =30.2° corresponding to interplanar distance of 0.296 nm. As the bath

temperature increased, the intensity of the peak (221) increased. This indicates that the grain

size increases when the bath temperature is increased.

Figure 5.4 X-ray diffraction patterns of Cu4SnS4 thin films deposited at various bath

temperatures (a) 25 C (b) 30 C (c) 35 C (d) 40 C (e) 45 C (f) 50 C [Cu4SnS4 (▲)]



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The Cu4SnS4 thin films were morphologically characterized using atomic force

microscopy (AFM). Figure 5.5 shows the three-dimensional representation of a 20 mm X 20

mm area of the Cu4SnS4 thin films deposited at different bath temperatures. It is observed

that the films deposited at 25 °C have a homogeneous, uniform surface and well cover the

substrate (Figure 5.5a). As the bath temperature was increased to 50 °C (Figure 5.5b),

decreasing in the number of grains could be observed. The grain size of Cu4SnS4 material is

much bigger with diameter around 1 mm.

a



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b

c



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d

e



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Figure 5.5 Atomic force microscopy images of Cu4SnS4 thin films deposited at various bath

temperatures (a) 25 C (b) 30 C (c) 35 C (d) 40 C (e) 45 C (f) 50 C

Figure 5.6 shows the absorption spectra of Cu4SnS4 films at various bath

temperatures. The films show a gradually increasing absorbance throughout the visible

region, which makes it possible for this material to be used in a photoelectrochemical cell.

The film deposited at 25°C showed gradual increasing of absorption starting from 650 nm

downward. This film showed higher absorption characteristics when compared to the films

prepared at other bath temperatures. Thus, this bath temperature is more preferable in the

preparation of Cu4SnS4 films of better quality on ITO substrate.

f



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Figure 5.6 Optical absorbance versus wavelength of the Cu4SnS4 films deposited at various

bath temperatures (a) 25 C (b) 30 C (c) 35 C (d) 40 C (e) 45 C (f) 50 C

5.3 Effect of solution concentration on the properties of films

The first set of experiment was carried out using constant concentration of 0.01 M of

SnCl2, Na2S2O3 and varying concentrations of CuSO4 (0.01 M – 0.02 M) solutions. The

second set of experiment was carried out using fixed concentration of 0.01 M of CuSO4,

Na2S2O3 and varying concentrations of SnCl2 (0.01 M – 0.02 M) solutions. The third set of

experiment was carried out using constant concentration of 0.01 M of CuSO4, SnCl2 and

varying concentrations of Na2S2O3 (0.01 M – 0.02 M) solutions. (deposition time=45 min, pH

1.5, deposition potential= -600 mV, deposition temperature=25 C).

Figure 5.7 shows the XRD patterns of the films deposited at various CuSO4

concentrations (0.01 M – 0.02 M) and constant Na2S2O3, SnCl2 at 0.01 M. There are six

Cu4SnS4 peaks at 2θ = 28.6°, 30.1°, 35.2°, 42.9°, 45.2° and 50.6° for the samples prepared at

0.01 M, 0.015 M and 0.02 M of CuSO4. The corresponding interplanar distances are 12, 2.96,



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2.54, 2.10, 2.00 and 1.80 Å, which attributed to the (102), (221), (420), (331), (512) and

(711) planes, respectively. However, as the concentration of CuSO4 was higher than 0.015 M

and 0.02 M, the copper sulfide peaks (Reference code: 000653556) which corresponding to

2.82 Å and 2.32 Å at 2θ = 31.8° and 38.8°, respectively were obtained.

Figure 5.7 XRD patterns of samples prepared at various CuSO4

concentrations: a – 0.01 M; b

– 0.015 M; c – 0.02 M. Concentration of SnCl2

and Na2S

2O

3 are fixed at 0.01 M.

(Cu4SnS

4 – ▲; CuS – ■)

Figure 5.8 shows the XRD patterns of the films deposited at various SnCl2

concentrations (0.01 M – 0.02 M) and fixed Na2S2O3, CuSO4 at 0.01 M. XRD indicates the

presence of six peaks at 2θ = 28.5°, 30.1°, 35.1°, 42.8, 45.2° and 50.5° belonging to Cu4SnS4

for samples prepared using lower concentrations (0.01 M and 0.015 M). There are no copper

sulfide peaks were observed from the samples deposited with 0.01 M of tin chloride. Six

peaks corresponding to interplanar distance of 3.12, 2.96, 2.55, 2.11, 2.01 and 1.80 Å were

observed for the film prepared from 0.02 M SnCl2.



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Figure 5.8 XRD patterns of samples prepared at various SnCl

2 concentrations: a – 0.01 M; b –

0.015 M; c – 0.02 M. Concentration of CuSO4

and Na2S

2O

3 are fixed at 0.01 M.

(Cu4SnS

4 – ▲; CuS – ■)

Figure 5.9 shows the XRD patterns of the films deposited at various Na2S2O3

concentrations (0.01 M – 0.02 M) with constant CuSO4, SnCl2 at 0.01 M. The thin films

prepared in different concentrations of Na2S2O3 showed six peaks at 2θ = 28.9°, 30.1°, 35.1°,

42.8°, 45.2° and 50.7°, corresponding to d-spacing values 3.08, 2.96, 2.55, 2.11, 2.01 and

1.79 Å, which attributed to the (102), (221), (420), (331), (512) and (711) planes, respectively

were detected. The appearances of copper sulfide peaks were detected when the

concentration of Na2S2O3 was higher at 0.015 M and 0.02 M.



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Figure 5.9 XRD patterns of samples prepared at various Na2S

2O

3 concentrations: a – 0.01 M;

b – 0.015 M; c – 0.02 M. Concentration of CuSO4

and SnCl2

are fixed at 0.01 M.

(Cu4SnS

4 – ▲; CuS – ■)

Figure 5.10 shows AFM images of films prepared at different CuSO4 concentrations

and constant SnCl2, Na2S2O3 at 0.01 M. The grain size for the film prepared at 0.015 M and

0.02 M are almost similar and do not much different from each other (Figure 5.10b and

Figure 5.10c). The crystal size decreases with the decrease of CuSO4 concentration (Figure

5.10a).



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(a)

(b



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Figure 5.10 Atomic force microscopy images of Cu4SnS

4 films deposited at various CuSO

4

concentrations: a – 0.01 M; b – 0.015 M; c – 0.02 M. Concentration of Na2S

2O

3

and SnCl2

are fixed at 0.01 M

(c)

(a)



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4 films deposited at various SnCl

2

concentrations: a – 0.01 M; b – 0.015 M; c – 0.02 M. Concentration of Na2S2O3 and

CuSO4 are fixed at 0.01M.

(b)

(c)



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(a)

(b)



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4 films deposited at various Na

2S

2O

3

concentrations: a – 0.01 M; b – 0.015 M; c – 0.02 M. Concentration of SnCl2

and CuSO4

are fixed at 0.01 M

Figure 5.11 shows the AFM images of films prepared at different SnCl2

concentrations and constant Na2S2O3, CuSO4 at 0.01 M. The images indicated that higher

concentration of SnCl2 leads to larger crystal size (Figure 5.11b and Figure 5.11c) while

lower SnCl2 exhibits smaller crystal size (Figure 5.11a). Meanwhile, the morphology of thin

films prepared under different concentrations of sodium thiosulfate was shown in Figure

5.12.

Figure 5.13 – 5.15 show the absorption spectra of Cu4SnS4 films at different

concentrations of CuSO4, SnCl2 and Na2S2O3, respectively. The films show a gradually

increasing absorbance throughout the visible region, which makes it possible for this material

to be used in a photoelectrochemical cell. From the graph, it is indicated that the samples

prepared at lower CuSO4, SnCl2 and Na2S2O3 concentration (0.01 M) have higher absorption

values respectively.

(c)



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Figure 5.13 Optical absorbance versus wavelength of the Cu

4SnS

4 films deposited at various

CuSO4

concentrations (0.01 M – 0.02 M). Concentration of SnCl2

and Na2S

2O

3

are fixed at 0.01 M

Figure 5.14 Optical absorbance versus wavelength of the Cu4SnS


SnCl2

concentrations (0.01 M – 0.02 M). Concentration of CuSO4

and Na2S

2O

3

are fixed at 0.01 M



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Figure 5.15 Optical absorbance versus wavelength of the Cu4SnS


Na2S

2O

3 concentrations (0.01 M – 0.02 M). Concentration of CuSO

4 and SnCl

2

are fixed at 0.01 M

5.4 Effect of deposition time on the properties of films

Based on the results obtained, we can conclude that the good quality of thin films was

deposited using 0.01 M of solutions concentration. Further experiments were carried out to

determine the effects of deposition time (15 to 60 min) towards the properties of thin films.

Other experimental conditions were not altered to maintain a constant approach towards

uniform set-up. (pH 1.5, deposition potential= -600 mV, solutions concentration=0.01 M,

temperature=25 C).

Figure 5.16 shows the X-ray diffraction patterns of films deposited at –600 mV versus

Ag/AgCl under room temperature for various deposition periods. There are two peaks,

observed at the diffraction angles of 27.6and 38.8 for the films deposited for 15 min of

deposition period. These two peaks were assigned to (002) and (222) plane, respectively.

Meanwhile, the films prepared at 30 min showed five peaks at 2 = 30.3, 35.1, 38.7, 45.3

and 50.5 corresponding to interplanar distances of 2.96, 2.54, 2.33, 2.00 and 1.80 Å

respectively. However, the films prepared at longer deposition period (45 min) showed only

four peaks at 2 = 30.3, 35.1, 43.3 and 50.4 corresponding to interplanar distances of



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2.96, 2.54, 2.07 and 1.80 Å, respectively. Further increases deposition time to 60 min reduced

in the number of Cu4SnS4 peak as shown in Figure 5.16d. All these peaks are related to the

compound of Cu4SnS4 (Reference code: 010710129) of orthorhombic structure. On the other

hand, the strongest peak occurred at 2 =30.1 with d=2.96 Å. It indicates that the preferred

orientation lies along the (221) plane for electrodeposited Cu4SnS4 thin films. The appearance

of copper sulfide (Reference code: 000653556) was detected at 2 = 31.5 for the films

deposited at 30 min, probably due to the Cu4SnS4 formation reaction is not complete during

electrodeposition process.

Figure 5.16 X-ray diffraction patterns of Cu4SnS4 thin films deposited at various deposition

periods (a) 15 min (b) 30 min (c) 45 min (d) 60 min [Cu4SnS4 (▼), CuS (■)]



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(a)

(b)



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(c)

(d)



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Figure 5.17 Atomic force microscopy images of Cu4SnS4 thin films deposited at various

deposition periods (a) 15 min (b) 30 min (c) 45 min (d) 60 min

The Cu4SnS4 thin films were morphologically characterized by using atomic force

microscopy. Figure 5.17 shows the three-dimensional representation of a 20 m X 20 m

area of the Cu4SnS4 thin film deposited at various deposition periods. It is indicated that the

deposited thin films are crystalline and their grain size varies with the different deposition

periods. The grain size decreases as the deposition period was increased from 15 min to 60

min. The average grain size of around 2.5 m and 0.8 m were observed on the film prepared

at 15 min (Figure 5.17a) and 60 min (Figure 5.17d) , respectively.

Figure 5.18 Difference between photocurrent and darkcurrent (Ip-Id) of Cu4SnS4 thin film

deposited at 25 C under various deposition periods. (a) 45 min

(b) 30 min (c) 15 min (d) 60 min

Figure 5.18 shows the difference between the photocurrent (Ip) and darkcurrent (Id)

versus potential for the deposited films in contact with Fe2+/Fe3+ solution. The current change

with illumination confirms that the films possess semiconducting properties. The films

prepared at 45 min showed the highest photoresponse activity as compared with other



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deposition periods. This could be due to sufficient material deposited onto surface of

substrate. The photocurrent occurs on the negative potential indicates that the films prepared

are of p-type semiconductor.

5.5 Effect of pH value on the properties of films

The best optimum deposition time was 45 minutes according to overall results.

Further experiments were carried out to determine the effects of pH (pH 1.1 to pH 2.0)

towards properties of thin films. Basically, the sodium thiosulfate is stable under neutral or

alkaline medium but unstable in acidic solution. Other experimental set-up was maintained as

before. (deposition time=45 min, deposition potential= -600 mV, solutions

concentration=0.01M, deposition temperature=25 C)

Figure 5.19 X-ray diffraction patterns of films prepared at different pH values

(a) pH 1.1 (b) pH 1.3 (c) pH 1.5 (d) pH 2.0 [Cu4SnS4 ]



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Figure 5.19 shows the XRD patterns of Cu4SnS4 thin films deposited under different

pH values ranging from 1.1 to 2.0. The XRD patterns were found to be polycrystalline with

orthorhombic structure. For the films prepared at pH 1.1, six peaks at 2 = 28.7, 30.2,

35.1, 39.0, 47.3 and 50.6 corresponding to interplanar distances of 3.11, 2.96, 2.56, 2.32,

1.93 and 1.81 Å, respectively were observed. As the pH was increased to 1.3 and 1.5, the

Cu4SnS4 peak increased to seven and finally nine, respectively. All these peaks are well

matched with the standard Joint Committee on Powder Data Standard pattern. However, as

the pH further increases to 2, the number of peaks reduced to six as can be seen in Figure

5.19d.

Figure 5.20 shows the three-dimensional representation of a 20 m X 20 m area of

the Cu4SnS4 thin films deposited at different pH values varied from 1.1 to 2.0. Larger grain

sizes were observed on the surface of Cu4SnS4 films deposited at pH 1.1 (Figure 5.20a) and

1.3 (Figure 5.20b). As the pH was increased to 1.5, the grain size of this film was much

smaller and has complete coverage over the substrate surface (Figure 5.20c). However, at

higher pH, the AFM image shows low appearance of grains over the surface of substrate as

shown in Figure 5.20d.

(a)



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(b)

(c)



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Figure 5.20 Atomic force microscopy images of Cu4SnS4 thin films prepared at different pH

values (a) pH 1.1 (b) pH 1.3 (c) pH 1.5 (d) pH 2.0

Figure 5.21 shows the absorbance spectra of Cu4SnS4 films at different pH values.

The film deposited at pH 1.5 produced the largest absorption value as compared with other

pH values. This response associated with the fact that more Cu4SnS4 materials were formed

at pH 1.5. This also indicated that the smaller grain size has complete coverage over the

substrate surface providing better absorption value. This result was consistent with the

observation from X-ray diffraction pattern and atomic force microscopy images. Thus,

deposition at pH 1.5 produced better quality of Cu4SnS4 films on ITO glass substrate.

(d)



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Figure 5.21 Optical absorbance versus wavelength of Cu4SnS4 films deposited at different pH

values (a) pH 1.5 (b) pH 1.3 (c) pH 1.1 (d) pH 2

The band gap energy and transition type was derived from mathematical treatment of

data obtained from optical absorbance versus wavelength with the following relationship for

near-edge absorption:

hv

EhvkA

n

g ][2/

(1)

where v is the frequency, h is the Planck’s constant, k equals to constant while n carries the

value of either 1 or 4. The value of n is 1 and 4 for the direct transition and indirect transition,

respectively. The band gap (Eg) could be obtained from a straight line plot of (Ahv)2/n as a

function of hv. The line to determine the band gap was plotted by using Microsoft Excel

software (least square method). The R2 value obtained from the graph shown is 0.9978 which

is almost to the value of 1. This value shows that all the data is fitted well by using this least

square method technique. Extrapolation of the line to the base line, where the value of

(Ahv)2/n is zero, will give Eg. The Figure 5.22 showed the band gap energy of Cu4SnS4 film

which prepared at pH 1.5 was 1.5 eV with direct transition.



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Figure 5.22 Plot of (Ahv)2/n versus hv when n=1 for Cu4SnS4 films deposited at pH 1.5

There are several reports have pointed out interesting semiconducting performances in

some terms of the Cu-Sn-S semiconductor compounds [1-30]. These materials have been

prepared by using various deposition methods. The obtained films have been investigated

using different tools in order to characterize physical, optical and electric properties.

References:

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