Elsevier

Electrochimica Acta

Volume 56, Issue 18, 15 July 2011, Pages 6406-6410
Electrochimica Acta

Photoelectrochemical performances of indium-doped CdS0.2Se0.8 thin film electrodes prepared by spray pyrolysis

https://doi.org/10.1016/j.electacta.2011.05.014Get rights and content

Abstract

Polycrystalline undoped and indium-doped CdS0.2Se0.8 thin films were deposited on FTO-coated glass substrates by spray pyrolysis. The cell configurations CdS0.2Se0.8/1 M (Na2S + S + NaOH)/C and In:CdS0.2Se0.8/1 M (Na2S + S + NaOH)/C were used to study a wide range of photoelectrochemical characteristics including capacitance–voltage in the dark, current–voltage characteristics in the dark and under illumination, photovoltaic power output and spectral response and to perform electrochemical impedance spectroscopy studies. The study reveals that the films exhibit n-type conductivity. Various PEC parameters such as the junction ideality factor under illumination, series and shunt resistances, fill factor and efficiency have been estimated for the PEC cells formed with CdS0.2Se0.8 and indium-doped CdS0.2Se0.8 thin films. The efficiency and fill factor of these PEC cells are found to be improved from 0.79% and 0.46 to 2.12% and 0.49, respectively, with indium doping in CdS0.2Se0.8 thin films. Electrochemical impedance spectroscopy studies show that doping of indium into CdS0.2Se0.8 thin film improves the performance of resulting PEC cells.

Highlights

► Polycrystalline undoped and indium doped CdS0.2Se0.8 thin films were deposited on FTO coated glass substrates by spray pyrolysis. ► The films are studied for various photoelectrochemical performance parameters. ► The study reveals that the films exhibit n-type conductivity. ► Efficiency and fill factor of PEC cell are found to be improve from 0.79% and 0.46 to 2.12% and 0.49, respectively, with indium doping in CdS0.2Se0.8 thin films. ► Electrochemical impedance spectroscopy study shows that doping of indium in CdS0.2Se0.8 thin film improves the performance of PEC cell.

Introduction

Due to rapid growth in the world economy, energy problems have attracted considerable attention in the past several decades [1]. To provide alternative energy sources, research has been targeted toward developing renewable energy sources, including solar, wind, nuclear, hydraulic and biomass energy. Among these alternatives, solar to electrical conversion systems have always been a fascinating and challenging frontier for science and technological applications [2]. To generate chemical energy in a form that can be stored from solar energy is thus an important goal for the development of clean energy. One method for achieving this goal is the use of a photoelectrochemical (PEC) solar cell. Semiconductor liquid junction solar cells have attracted a great deal of attention in recent years due to the growing interest in solar energy conversion [3], [4]. To develop a useful PEC solar cell, a principal requirement is that the photoanode or photocathode should have a bandgap whose energy closely corresponds to the maximum light intensity in the visible spectrum to utilize the solar spectrum efficiently; second, the semiconductor electrodes must be stable with respect to photocathodic/photoanodic reactions [5], [6].

CdS1  xSex is a II–VI–VI ternary semiconductor with a wide range of band gaps (CdSe = 1.74 eV and CdS = 2.44 eV) and is used in applications in various optoelectronic devices. In the CdS1 xSex system, the CdS0.2Se0.8 thin film has the lowest resistivity and activation energy [7] and shows better photoelectrochemical properties [8]. To decrease the resistivity as well as the bandgap of this material and increase the efficiency of the PEC cells, the material must be doped with suitable dopants such as indium. Many groups have reported the properties of the undoped and doped II–VI thin films prepared by a variety of techniques, including hot wall deposition [9], [10], the doctor blade technique [11], the solvothermal route [12], electrodeposition [13], [14], [15], chemical bath deposition [16], [17], chemical vapor deposition [18], spray pyrolysis [5], [7], [19], [20] and others. Among the various deposition techniques which are available for the preparation of thin films, spray pyrolysis, which has the advantages of low cost, ease-of-use, safety and the possibility for implementation in a standard laboratory, is suitable for many scientific studies and technological applications. This method is based on the preparation of salt solutions of the material from which the films are to be prepared.

This paper is focused on the deposition and PEC characterization of undoped and indium-doped CdS0.2Se0.8 thin films with respect to a number of parameters, namely, open-circuit voltage (Voc), short-circuit current (Isc), efficiency (η), fill factor (FF), flat band potential (Vfb), charge-transfer impedance (Rct) and the double layer capacitance associated with the charge transfer process (Cct).

Section snippets

Preparation of undoped and indium-doped CdS0.2Se0.8 thin films

Polycrystalline undoped and indium-doped CdS0.2Se0.8 thin films were deposited on FTO-coated glass substrates by spray pyrolysis at an optimized substrate temperature of 300 °C [7]. Aqueous solutions (0.025 M) of cadmium chloride dehydrate (CdCl2·H2O), thiourea ((NH2)2CS) and selenourea ((NH2)2CSe) and various concentrations of InCl3 were used as starting materials. A spray rate of 3 ml/min was kept constant throughout the experiment. The distance between the nozzle and the substrate was 28 cm. Air

Results and discussion

The crystal structures of the undoped and indium-doped CdS0.2Se0.8 thin films have been determined by X-ray diffraction. The diffractograms of both undoped and indium-doped CdS0.2Se0.8 thin films have been reported elsewhere [21]. The diffractograms indicated the presence of a hexagonal wurtzite crystal structure. An improvement in crystallinity has been observed with indium doping. Crystallite size was estimated using Scherrer's formula by measuring the peak width very precisely and comparing

Conclusions

In conclusion, the spray deposition of undoped and indium-doped CdS0.2Se0.8 thin films on conducting FTO-coated glass substrates is possible using the simple and inexpensive spray pyrolysis technique. A PEC cell formed with a indium-doped CdS0.2Se0.8 photoanode gives better performance than that of a pure CdS0.2Se0.8 photoanode. These studies reveal that both CdS0.2Se0.8 and indium-doped CdS0.2Se0.8 thin films show n-type conductivity. The efficiency (η, %) and FF are found to increase from

Acknowledgement

One of the authors, A.A. Yadav, is grateful to the University Grants Commission, New Delhi (West regional office, Pune), India, for financial assistance through the minor research, Project no. F. 47-656/2008.

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