Nanostructured Photocathodes for Infrared Photodetectors and Photovoltaics

Abstract

Interfacial energy band alignment is crucial for applications involving charge transfer and transport. Specifically, efficient photovoltaic (PV) devices require fine-tuning of the energy levels at interfaces between the absorber and the electrodes for extraction of photogenerated charges. Infrared (IR) absorbers have a small bandgap, hence such tuning is difficult using common electrode materials. Semiconductor sensitized PV devices typically utilize transparent metal oxide photoanodes, since many semiconductor absorbers can inject photoexcited electrons into their conduction bands. Transparent photocathode electrodes, to which photoexcited holes are transferred from semiconductor absorbers, are less common. Transparent nanostructured photocathodes with beneficial energy level alignment with small bandgap semiconductors can widen the material choices for IR photoelectrodes. Herein we show that CuSCN nanowire (NW) arrays can serve as such photocathodes, with efficient transfer of photogenerated holes from bulk-like PbS absorbing in the IR and near-IR range. Pulsed electrodeposition was used to fabricate high-quality CuSCN NW arrays. Significant NIR and IR photocurrents showed that the CuSCN NW array is an efficient photocathode for PbS sensitized IR photovoltaic devices. Comparison of various electrode materials verified the photogenerated hole injection vs competing processes such as electron injection and recombination and suggested that this material system can be used for studying photosensitized hole injection from other small bandgap semiconductors.