Photovoltaic properties of n-CdS_1−xTe_x thin film/polysulphide photoelectrochemical solar cells prepared by chemical bath deposition

Abstract

n-CdS_1−xTe_x (0≤x≤1) thin films were deposited by a chemical bath deposition technique on highly conducting, precleaned stainless steel substrates and were used in a photoelectrochemical conversion process. The as-grown films exhibited photoactivity in an aqueous 0.5 M NaOH+0.5 M Na₂S+0.5 M S (pH 12.6) electrolyte. An interface between n-CdS_1−xTe_x semiconductor photoelectrode and an electrolyte redox couple was formed and investigated through the capacitance–voltage, current–voltage and photovoltaic characteristics. A brief discussion is made on the properties of the semiconductor/electrolyte Schottky barrier with reference to the experiments performed and the photoelectrode composition. The observed results on the capacitance–voltage and current–voltage measurements in dark are compared with the photovoltage measurements. The measurements on the characteristic photovoltaic properties showed a significant enhancement in the cell performance after addition of Te in to CdS (x=0.1).

Introduction

Photovoltaic has emerged as a fast developing field due to the global search for alternative sources for power generation. Ever-abundant solar energy can be harnessed by suitable devices called photovoltaic cells or solar cells for low-cost conversion of solar radiations into electrical energy. Thin film based photoelectrochemical solar cells have wide applications due to their low fabrication cost, high-throughput processing techniques and ease of junction formation with an electrolyte. Among the materials that have attracted attention in thin-film polycrystalline form are II–VI and I–III–VI₂ ternaries and multiternaries. These semiconductor materials are attractive especially in thin film solar cell application, because of their high optical absorption (≥10⁴ cm⁻¹) and their versatile optical and electrical properties. These electrical and optical properties can suitably be tailored and tuned to the specific need in a given device structure. Among the Cd-chalcogenide group, the most prominent is the Cd–S–Te ternary alloy, the band gap of which can be tailored close to the solar-energy maximum (≅1.4 eV) [1], [2], [3], [4], [5]. In this context, a ternary chalcogenide, especially CdS_1−xTe_x has an added advantage of tailoring the band gap to cope with the visible spectrum [6], [7], [8], [9]. We, therefore, planned and propose through these investigations to synthesize CdS_1−xTe_x thin composite layers of variable composition and to use them in photoelectrochemical application. The electrochemical performance of the cells deviced out of these electrodes has been examined as a function of the electrode composition and correlated with the various materials properties.