(Photo)electrochemical analysis of electrosynthesized fibrous cadmium indium selenide (CdIn2Se4) thin films

https://doi.org/10.1016/j.jphotochem.2016.12.010Get rights and content

Highlights

  • Obtained highest efficiency for the electrodeposited CdIn2Se4 photoanode in PEC cell.

  • Analysis of photoanode performance using electrochemical impedance spectroscopy.

  • Theoretical modeling of energy band diagram to analyze performance of PEC cell.

Abstract

Electrosynthesized cadmium indium selenide (CdIn2Se4) thin films were (photo) electrochemically analyzed by current–voltage characteristics, photoresponse, speed response, electrochemical impedance study, and capacitance–voltage characteristics. The improved photoconversion efficiency of electrosynthesized CdIn2Se4 thin film-based photoelectrochemical cell explained with the help of theoretical modeling of energy band diagram and equivalent circuit model of the impedance spectra of the photoelectrochemical cell.

Introduction

The interest in (photo)electrochemical analysis has increased due to the availability of sophisticated instrumentation, such as electrochemical impedance spectroscopy (EIS) [1], [2]. Many researchers have used impedance spectroscopy to elucidate the electrode processes, to examine dye-sensitized solar cells [3], [4], for a photoelectric investigation of charge transferring metal-doped fullerenes, for the analysis of water splitting [5], and for the analysis of water oxidation by photoelectrochemical investigations [6]. Despite this, there are few reports on the electrochemical analysis of chalcogenide semiconductors.

Cadmium indium selenide (CdIn2Se4) is a ternary chalcogenide compound belonging to the II–III–VI group [7]. The material has been successfully used as absorber layer because of its light harvesting property with a narrow direct band gap and low electrical resistivity to construct a variety of electronic and electro-optical devices. One of its competent utilization is in thin film heterojunction solar cells or as a photoelectrode in photoelectrochemical (PEC) cells. Effective exploitation of solar energy is the most promising way to address issue of energy crisis. Therefore, efficient solar energy conversion into usable photo-voltage by PEC cells has inspired tremendous research efforts.

The pioneering work by many researchers reported variety of techniques, such as vacuum evaporation [7], slurry pasting [8], thermal evaporation [9], Bridgmann method [10], spray pyrolysis [11], [12], [13], chemical bath [14], pulsed electrodeposition [15], and electrodeposition [16], [17], [18], [19], [20] for synthesis of CdIn2Se4 thin films. Most of these studies were related to the structural and optical properties of CdIn2Se4 thin films. In previously reported study, the photoelectrochemical properties of CdIn2Se4 thin films were examined by Nikale et al. and Ahn et al. [13], [17]. Ahn et al. [17] reported an electrodeposited CdIn2Se4 photoanode with a conversion efficiency of 0.42%, which is the highest efficiency reported thus far for an electrodeposited CdIn2Se4 photoanode. Based on prior work we recognize that CdIn2Se4 photoanode is sensitive to particle size. This would allow us to explore the relationship between light harvesting and absorbance spectra as a function of band gap and particle shape. Thus, in present paper, we report the results of an investigation of properties of PEC cell. The current-voltage (I–V) characteristics of PEC cell used to determine cell efficiency. Transient photoresponse and speed response study determines stability of material and diffusion coefficient of minority careers. Mott-Schottky plot was used to determine flat band potential and charge carrier density of CdIn2Se4 photoelectrode and hence to model energy band diagram. In addition, EIS was carried out to examine the carrier transport properties, to determine the equivalent circuit parameters and to analyze the performance of the PEC cell. The possible origin for the relatively poor performance of the material is discussed.

Section snippets

Materials and synthesis

The electrochemical approach used to synthesize CdIn2Se4 thin films was identical with that of Mahalingham and Wagh [18], [20]. Briefly, thin films were first potentiostatically deposited on the stainless steel substrate (working electrode) using a Battery Cycler unit. To complete three-electrode configuration, graphite rod was used as counter electrode and standard calomel electrode (SCE) as reference electrode. The effective working electrode area was 1 cm2. Fiber growth was done by aqueous

Optical absorbance study

The optical absorption spectrum of the CdIn2Se4 thin film examined over the wavelength range, 350 nm–850 nm is shown in Supplementary data Fig. S3 inset. The CdIn2Se4 thin film has high absorption in the visible region with a hump at 725 nm, making it a good light absorbing material. The optical band gap spectrum was plotted from the absorption spectrum. Fig. S3 shows the linear variation of (αhυ)2 versus (hυ), which indicates that the material has a direct optical band gap [25]. The straight-line

Conclusions

The optical and photovoltaic performance of electrosynthesized CdIn2Se4 semiconductor fibers in the form of porous thin film electrode on cost effective stainless steel substrate has been studied for PEC cell containing the polysulfide electrolyte. The PEC performance of the cell showed a good photoresponse, comparatively high short circuit current and open circuit voltage with better stability over long duration with lower value of diffusion coefficient and high value of carrier lifetime to

Acknowledgements

One of the authors, Dr. B. G. Wagh, gratefully acknowledges the contribution of the University of Pune, Research fund under the BCUD Scheme. In addition, this research was supported by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2014R1A6A1031189).

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