www.elsevier.com/locate/matlet

Materials Letters 59 (2

Copper selenide thin films prepared using combination of chemical

precipitation and dip coating method

Zulkarnain Zainal*, Saravanan Nagalingam, Tan Chin Loo

Department of Chemistry, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

Received 12 April 2004; accepted 13 December 2004

Available online 12 January 2005

Abstract

A novel method has been developed for the preparation of copper selenide thin films. The method is based on a combination of chemical

precipitation of copper selenide powders and a dip coating technique using this powder. The synthesized powder and deposited thin films at

various dip coatings were analyzed using X-ray diffractometry and scanning electron microscopy (SEM). X-ray diffraction data of the thin

films indicate formation of polycrystalline materials. The SEM micrographs showed formation of compact and granular morphology for the

film deposited after four dip coatings. The thin films produced were found to display p-type semiconductor behavior.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Copper selenide; Thin films; Semiconductors; Photoelectrochemical cell; Metal chalcogenide; Dip coating

1. Introduction

Intensive research has been performed in the past to

study the deposition and characterization of semiconducting

metal chalcogenide thin films. They are considerable

interest in the field of solar selective coating, optoelectronic

devices, electronics and electrical devices. Copper selenide

is a semiconducting material, which has a number of

applications in solar cells, super ionic conductors and

photo-detectors [1–4]. These materials are semiconductors

with p-type conductivity. Copper selenide usually exists as

copper (I) selenide (Cu2Se or Cu2�xSe) [5–10] or copper (II)

selenide (CuSe or Cu3Se2) [11–14]. Copper (II) selenide in

Cu3Se2 form is often reported as an impurity phase along

with CuSe phase [11,14]. A number of methods have been

reported for the deposition of copper selenide thin films of

different crystalline modifications and varying stoichiome-

tries including various preparation techniques such as a

flash evaporation [15], selenisation [16], vacuum evapo-

ration [17], a solid state reaction [18] and a chemical bath

deposition [6,7,19].

0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.matlet.2004.12.044

* Corresponding author. Tel.: +60 389466810; fax: +60 389435380.

E-mail address: zulkar@fsas.upm.edu.my (Z. Zainal).

In this paper, we report a relatively new, combination of

chemical precipitation and dip coating method to produce

copper selenide thin films with mixed phases. The paper

deals with preparation, characterization and the photo-

electrochemical properties of the copper selenide thin films

prepared by this method.

2. Experimental procedures

The chemicals were of Analar grade and used as obtained

without further purification. All the solutions were prepared

using deionised water. CuSe powders were synthesized by

chemical method. The desired amount of elemental sele-

nium was dissolved in a NaOH (12 M) solution and stirred

rapidly for 20 min. Upon complete dissolution of elemental

selenium, Cu2+ solution was added and the rapid stirring

process was maintained for almost 15 min. Black precipitate

obtained was centrifuged and washed with distilled water

and dried in oven for 1 h. Polyethylene glycol dissolved in

ethanol was used as a medium for the dip coating method.

To this solution, a required amount of synthesized powder

and diethanolamine was mixed under rapid stirring. Indium

doped tin oxide (ITO) glass was used as the substrate to

005) 1391–1394

Table 1

The comparison between JCPDS data (File No. 06-0427) and experimen-

tally observed values for CuSe powders

2h (8) d-spacing (2) hkl Compound

Observed values JCPDS data

26.6 3.35 3.35 101 CuSe (hexagonal)

28.2 3.17 3.18 102 CuSe (hexagonal)

29.8 2.99 2.94 103 CuSe (hexagonal)

31.1 2.87 2.88 006 CuSe (hexagonal)

41.1 2.19 2.19 106 CuSe (hexagonal)

46.1 1.97 1.97 110 CuSe (hexagonal)

50.1 1.82 1.82 108 CuSe (hexagonal)

53.9 1.70 1.70 201 CuSe (hexagonal)

54.9 1.67 1.67 202 CuSe (hexagonal)

56.6 1.62 1.62 116 CuSe (hexagonal)

Z. Zainal et al. / Materials Letters 59 (2005) 1391–13941392

deposit the thin films. The ITO glass was dipped in the

solution and withdrawn to produce a gel-coated film. The

coatings were dried at 100 8C for 30 min. The films formed

were further heated in air at 500 8C for 30 min in an electric

furnace. The process was repeated to obtain films with

different number of coatings.

X-ray diffraction (XRD) analysis was carried out using a

Philips PM 1730 Diffractometer for the 2h ranging from 28to 608 with CuKa line (k=1.5418 2) used as an incident

beam. Scanning electron microscope (SEM) analysis was

performed on a JEOL JSM 6400 Scanning Microscope.

Photoelectrochemical (PEC) tests were run in Na2S2O3

(0.01 M) solution by running linear sweep voltammetry

(LSV) between �0.10 V and �1.00 V. An EG&G Princeton

Applied Research potentiostat driven by a software model

270 Electrochemical Analysis System was used to control

the LSV process and to monitor the current and voltage

profiles in a conventional three-electrode cell. Ag/AgCl was

used as the reference electrode. The working and counter

electrodes were made up of copper selenide coated ITO

glass substrate and platinum, respectively. The counter

electrode was polished prior to the insertion into the

electrolytic cell. A tungsten–halogen lamp (100 W) was

used for illuminating the electrode. The photocurrent (Ip)

and dark current (Id) for the films were obtained.

(a)

3. Results and discussion

Fig. 1 shows the XRD plot of the copper selenide powder

obtained through the chemical precipitation method. All the

30 40 50 60

116

202201

108

110

106

006

103

102

101

2θ/degrees

Inte

nsity

(ar

bitr

ary

units

)

Fig. 1. XRD plot of copper selenide powder.

peaks obtained are well matched with the Joint Committee

on Powder Diffraction Standards (JCPDS) data (File No.

06-0427) (Table 1). Orientation along (110) plane was found

to be most prominent. The observed data obtained indicate

hexagonal phase of CuSe was formed by this method. No

selenium peaks or unassigned peaks are observed indicating

that the CuSe powder obtained is pure without existence of

any impurity.

Fig. 2 shows the SEM micrographs of CuSe powder at

different magnifications. At lower magnification, fine

granules are observed. The sizes of the granules vary from

0.5 to 1.5 Am. The granules exist in an agglomerated form

(b)

10µm EHT = 15.00 kVMag = 1.00 KX

WD = 6 mmEMUPM

Signal A = SE1 Date :17 Jun 2003Time :16:27:21

1µm EHT = 30.00 kVMag = 8.00 KX

WD = 10 mmEMUPM

Signal A = SE1 Date :10 Jul 2003Time :14:06:46

Fig. 2. SEM micrograph of CuSe powder at different magnification (a) x

1000 (b) x 8000.

30 40 50

4 dip

3 dip

2 dip

1 dip

∆

∆

∆

◊

◊

◊

◊

2θ/degree

Inte

nsity

(A

rbita

ry u

nits

)

Fig. 3. XRD patterns of copper selenide thin films obtained at different

number of dip coatings; CuSe2 (x), Cu2Se (w) and CuSe (j).

(a)

Z. Zainal et al. / Materials Letters 59 (2005) 1391–1394 1393

and display a compact morphology. At higher magnification,

the granules were found to display flake like morphology on

the outer shell. Fig. 3 shows the XRD patterns of the copper

selenide thin films prepared at different number of dip

Table 2

Comparison between the JCPDS data (File No. CuSe-06-0427, CuSe2-37-

1187, Cu2Se-26-1115) and experimentally observed values for the copper

selenide thin films obtained at different number of dip coatings

Number 2h (8) d-spacing (2) Compounds

of dipsObserved

values

JCPDS

data

1 32.5 2.75 2.74 CuSe2 (cubic)

35.5 2.52 2.50 CuSe2 (cubic)

38.7 2.32 2.32 Cu2Se (orthorhombic)

48.8 1.86 1.84 CuSe2 (cubic)

53.5 1.71 1.70 CuSe (hexagonal)

2 32.6 2.74 2.74 CuSe2 (cubic)

35.6 2.52 2.50 CuSe2 (cubic)

38.8 2.32 2.32 Cu2Se (orthorhombic)

48.8 1.86 1.84 CuSe2 (cubic)

53.5 1.71 1.70 CuSe (hexagonal)

3 32.5 2.75 2.74 CuSe2 (cubic)

35.5 2.52 2.50 CuSe2 (cubic)

38.7 2.32 2.32 Cu2Se (orthorhombic)

48.8 1.86 1.84 CuSe2 (cubic)

53.5 1.71 1.70 CuSe (hexagonal)

4 32.5 2.74 2.74 CuSe2 (cubic)

35.6 2.52 2.50 CuSe2 (cubic)

38.7 2.32 2.32 Cu2Se (orthorhombic)

48.9 1.86 1.84 CuSe2 (cubic)

53.5 1.71 1.70 CuSe (hexagonal

coatings. Three phases of copper selenide are formed,

namely, CuSe2 (cubic), Cu2Se (orthorhombic) and CuSe

(hexagonal). The CuSe2 phase remained the most prominent

phase producing three peaks at all levels of dip coatings with

the most prominent peak obtained at 2h=35.58 correspond-ing to interplanar distance of 2.52 2 (Table 2). Peaks

attributable to Cu2Se and CuSe phases were obtained for all

the films. As the number of dip coating increased, the

intensity of the peaks increased. The sharp shape of the peaks

indicates that the materials formed are polycrystalline in

nature. The peak corresponding to the formation of CuSe

was less dominant compared to other phases of copper

selenide. The data obtained from the XRD plot confirms the

fact that copper selenide undergoes phase transformation

upon heating as reported by other researcher [20].

Fig. 4 shows the SEM micrographs of the thin films

prepared at one and four dip coatings. The film obtained

after one dip coating presents less compact morphology

due to less materials deposited on the surface of the

substrate. The sizes of the granules are almost uniform

spanning from 1 to 1.3 Am. The film obtained after four

dips coating exhibit compact morphology with the sizes of

the granules varying between 1 and 1.5 Am. The compact

morphology is due to number of coatings applied which

increased the quantity of the materials deposited on the

substrate.

1µm

(b)

1µm

Fig. 4. SEM micrograph of copper selenide thin films deposited at different

number coatings: (a) 1-dip and (b) 4-dip coatings.

0

0.15

0.30

0.45

0.60

-1.2-0.9-0.6-0.3

(b)

(c)

(a)

Potential (V vs Ag/AgCl)

I(m

A)

Fig. 5. The photoresponse of the samples: (a) Darkcurrent of the films (b)

Photocurrent of film deposited after 2 dip coatings and (c) Photocurrent of

film deposited after 4 dip coatings.

Z. Zainal et al. / Materials Letters 59 (2005) 1391–13941394

Fig. 5 shows the photoresponse of the copper selenide

films prepared by the dip coating method after two and four

dips in the presence of Na2S2O3 upon illumination with a

halogen lamp (100 W). An increase in the current could be

observed as the films are illuminated. The photoresponse

upon illumination indicates that the films are sensitive

towards light supporting a semiconductor behavior. The

films obtained after four dip coatings produced the highest

photoresponse compared to the film deposited after two dip

coatings. This is due to the high amount of material

deposited onto the substrate at this coating sequence. The

fact that the photocurrent occurs on the negative (cathode)

potential area indicates that the films prepared are of p-type

(positive) [21–26]. The films could be deployed as photo-

cathode in the photoelectrochemical cell application to

facilitate a reduction reaction of the electroactive species

in the solution.

4. Conclusions

Polycrystalline copper selenide thin films with mixed

phases could be deposited using combination of chemical

precipitation and dip coating method. The method

employed is cheap and less time-consuming compared to

other conventional method. The XRD data confirms

formation of polycrystalline materials. The SEM micro-

graphs show the deposition of compact granular morphol-

ogy. The photoresponse behavior of the films indicates that

the material could be used as a detector in the optical

devices operating in the visible region of the solar

spectrum.

Acknowledgements

The authors would like to thank the Malaysian Govern-

ment for funding this project under IRPA Grant No. 09-02-

04-0369-EA001. We also thank the Department of Chem-

istry, Universiti Putra Malaysia for the provision of

laboratory facilities.

References

[1] H.M. Pathan, C.D. Lokhande, D.P. Amalnerkar, T. Seth, Appl. Surf.

Sci. 211 (2003) 48.

[2] W.S. Chen, J.M. Stewart, R.A. Mickelson, Phys. Lett. 46 (1985) 1095.

[3] H. Okimura, T. Matsumae, R. Makabe, Thin Solid Films 71 (1980)

53.

[4] H.M. Pathan, C.D. Lokhande, D.P. Amalnerker, T. Seth, Appl. Surf.

Sci. 9875 (2003) 1.

[5] S.K. Haram, K.S.V. Santhanam, M. Neumann-Spallart, C. Levy-

Clement, Res. Bull. 27 (1992) 1185.

[6] G.K. Padam, Thin Solid Films 150 (1987) L89.

[7] C. Levy-Clement, M. Neumann-Spallart, S.K. Haram, K.S.V. Santha-

nam, Thin Solid Films 302 (1997) 12.

[8] A. Toneje, A.M. Toneje, J. Solid State Chem. 39 (1981) 259.

[9] R.B. Shafizade, I.V. Ivanova, M.M. Kazinets, Thin Solid Films 35

(1976) 169.

[10] S. Kashida, J. Akai, J. Phys. C. Solid State Phys. 21 (1988) 5329.

[11] C.A. Estrada, P.K. Nair, M.T.S. Nair, R.A. Zingaro, E.A. Meyers,

J. Electrochem. Soc. 141 (1994) 802.

[12] A. Mondal, P. Pramanik, J. Solid State Chem. 47 (1983) 81.

[13] A. Mondal, P. Pramanik, J. Solid State Chem. 55 (1984) 116.

[14] R.B. Shafizade, I.V. Ivanova, M.M. Kazinets, Thin Solid Films 55

(1978) 211.

[15] B. Tell, J.J. Weigang, J. Appl. Phys. 48 (1977) 5321.

[16] T.L. Chu, S.S. Chu, S.C. Lin, J. Yue, J. Electrochem. Soc. 131 (1984)

2182.

[17] W.S. Chen, J.M. Stewart, R.A. Mickelson, Appl. Phys. Lett. 46 (1985)

1.

[18] I.P. Parkin, Chem. Soc. Rev. 25 (1996) 199.

[19] J.G. Garg, R.P. Sharma, K.C. Sharma, Thin Solid Films 164 (1988)

269.

[20] V.M. Garcia, P.K. Nair, M.T.S. Nair, J. Cryst. Growth 203 (1999) 113.

[21] M. Sharon, K. Basavaswaran, Sol. Cells 20 (1987) 323.

[22] K. Anuar, Z. Zainal, M.Z. Hussein, N. Saravanan, I. Haslina, Sol.

Energy Mater. Sol. Cells 73 (4) (2002) 351.

[23] K.K. Mishra, K. Rajeshwar, J. Electroanal. Chem. 273 (1989) 69.

[24] K. Rajeshwar, Adv. Mater. 4 (1992) 23.

[25] J.P. Rai, Sol. Energy Mater. Sol. Cells 30 (1993) 119.

[26] Z. Zainal, M.Z. Hussein, A. Ghazali, Sol. Energy Mater. Sol. Cells 40

(1996) 347.