Substrate effect on photocurrent enhancement of electrodeposited n-type Cu2O thin films

Abstract

Cuprous oxide (Cu2O) is a metal-oxide semiconductor with a band gap of about 2 eV, which has attracted interest because of its potential applications in solar energy conversion, catalysis and gas sensors. Such applications and emerging applications of Cu2O thin films in other areas make it worthwhile to study the electro-optical characteristics of Cu2O thin films extensively (Olsen et al., 1982). Fabrication of Cu2O thin films using electrodeposition is advantageous over the other techniques as this process includes low temperature, economy, simplicity and possibility of making large area thin films. Also, adjusting the deposition parameters during electrodeposition allows the conductivity type and the film morphology to be controlled as required (Lee et al., 2006; Rai 1988). The currently reported photovoltaic conversion efficiencies of good Cu2O based solar cells have remained in the range of 1-2 % which is far below the theoretical value. Barrier height measurements in various Schottky barrier solar cells have shown that values are always in the range 0.7-0.9 eV regardless of the substrate which forms the back contact of the cell. This is believed to be the principal cause of the low performance of the Cu2O Schottky barrier solar cells (Abdu, 2009). Therefore, the selection of a better substrate (metal or condcutive coating) for the junction formation is considered to be the most important factor. Metals with high work functions such as Ni and Pt, are considered to be such candidates for the n-Cu2O Schottky junction solar cells. Cost-wise Ni can be considered a better material as opposed to Pt which is highly expensive.