Fabrication and characterization of electrodeposited nanocrystalline/microcrystalline cuprous oxide thin films

Abstract

The quest and need for clean and economical energy sources have increased interest in the development of solar energy applications. In particular, direct conversion of solar energy to electrical energy and chemical energy using semiconductor photoelectrodes has attracted attention for many decades. Among the various metal oxide materials for solar energy applications, a promising material is cuprous oxide (Cu2O) and is one of the oldest known semiconductors. It is low cost and non toxic and its component elements are readily available. It has a direct band gap of about 2 eV and a high optical absorption coefficient. Nanocrystalline thin films increase the effective surface area of the films as compared with the microcrystalline thin films. Therefore preparation of nanoparticles of Cu2O is of special importance to improve the solar energy conversion efficiency. In this study, Cu2O films were deposited electrochemically on Ti substrates. In this study, a simple electrochemical technique was developed to fabricate the Cu2O/CuxS heterojunction to be used in a thin film photovoltaic solar cell. Electrodeposited Cu2O thin films on Ti substrates were sulphided by directly applying an aqueous solution of Na2S on to Cu2O films and annealed at 200 0C for a few minutes. Then the samples were exposed to NH4S gas for a few seconds. It was observed that the photovoltaic properties and the diode characteristics of nano/micro/Cu2O/CuxS structures were better than that of micro/Cu2O/CuxS structures. The maximum conversion efficiency of the micro/Cu2O/CuxS cell was 0.12% (Voc= 240 mV, and Isc= 0.86 mA/cm2) and that of the nano/micro/Cu2O/CuxS cell was 0.28% (Voc= 420 mV, and Isc= 2.1 mA/cm2) under AM1.5 illumination.