Fabrication and characterization of electrodeposited nanocrystalline/microcrystalline cuprous oxide thin film solar cells

Abstract

The quest and need for clean and economical energy sources have increased interest in the development of solar energy application. 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 application, a promising material is cuprous oxide (Cu20) 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 e V 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 Cu2 0 is of special importance to improve the solar energy conversion efficiency. In this study, Cu20 films were deposited electrochemically on Ti substrates. In our investigation, we have developed a simple electrochemical technique to fabricate the Cu20/CuxS heterojunction and used it to prepare a thin film photovoltaic solar cell. Electrodeposited Cu20 thin films on Ti substrates were sulphided by directly applying an aqueous solution of Na2S on to Cu20 films and annealed at 200 °C 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/Cu20/CuxS structures were better than that of micro/Cu20/CuxS structures. The maximum conversion efficiency of the micro/Cu20/CuxS cell was 0.12% (Voc= 240 m V, and Isc= 0.86 mA/cm 2 ) and that of the nano/micro/Cu20/CuxS cell was 0.28% (Voc= 420 m V, and I,c= 2.1 mA/cm 2 ) under AM1.5 illumination.