Doping and orientation regulation of p-type Cu:CdS1−xSex/Pt thin film photocathodes for enhanced photoelectrochemical water splitting

Abstract

Previously, we have demonstrated a series of p-type CdS1−xSex thin film photocathodes with high stability for scavenger-free photoelectrochemical (PEC) water splitting via Cu doping [1]. However, the incorporation of pre-deposited Cu atoms into CdS1−xSex thin films grown by gas-flow physical vapor deposition in furnace tube imposed a challenge on doping effectiveness and film quality, which consequently hindered PEC performance. In this work, a two-step growth protocol was developed by firstly co-evaporating precursors in a vacuum system and secondly annealing the precursors at high temperature under protection of high environmental pressure. The effective and uniform Cu doping was achieved due to the co-evaporation of Cu atoms during deposition of CdS1−xSex precursors. With this method, the p-type conductivity from Cu doping and the film orientation can be regulated. As a result, the two-step grown Cu:CdS1−xSex/Pt (x = 0.25) photocathode has demonstrated more efficient charge transport, with a photocurrent as high as 1.4 mA/cm2 for hydrogen evolution in scavenger-free 0.1 M Na2SO4 (aq) electrolyte, which was about 75% enhancement over the best previously reported Cu:CdS1−xSex/Pt photocathodes [1]. This study can shed light towards effective approach to fabricate efficient II–VI group thin film photocathodes.