Formation of high-density CuBi2O4 thin film photocathodes with polyvinylpyrrolidone-metal interaction

We present a polymer-assisted spin coating process used to fabricate high-density p-type CuBi2O4 (CBO) thin films. Polyvinylpyrrolidone (PVP) is introduced in the precursor solutions in order to promote uniform nucleation of CBO and prevent formation of the secondary phase, such as Bi2O3, by Bi3+ ion hydrolysis. Slow PVP molecule decomposition during the two-step annealing process, with a 1 M/0.5 M (Bi3+/Cu2+) metal ion concentration, enables optimum contact at the CBO/substrate interface by avoiding formation of voids. This resulted in the formation of non-porous, compact CBO thin films. The highest current density of the photoelectrochemical (PEC) oxygen reduction reaction is obtained with non-porous, compact CBO thin films due to unimpeded charge transport through the CBO bulk, as well as across the interface. When combined with silicon, the high-density CBO thin film investigated in this work is expected to provide new PEC tandem cell options to use for solar applications. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement