Solution phase treatments of Sb2Se3 heterojunction photocathodes for improved water splitting performance.

ABSTRACT

Antimony selenide (Sb2Se3) is an auspicious material for solar energy conversion that has seen rapid improvement over the past ten years, but the photovoltage deficit remains a challenge. Here, simple and low-temperature treatments of the p-n heterojunction interface of Sb2Se3/TiO2-based photocathodes for photoelectrochemical water splitting were explored to address this challenge. The FTO/Ti/Au/Sb2Se3 (substrate configuration) stack was treated with (NH4)2S as an etching solution, followed by CuCl2 treatment prior to deposition of the TiO2 by atomic layer deposition. The different treatments show different mechanisms of action compared to similar reported treatments of the back Au/Sb2Se3 interface in superstrate configuration solar cells. These treatments collectively increased the onset potential from 0.14 V to 0.28 V vs. reversible hydrogen electrode (RHE) and the photocurrent from 13 mA cm-2 to 18 mA cm-2 at 0 V vs. RHE as compared to the untreated Sb2Se3 films. From SEM and XPS studies, it is clear that the etching treatment induces a morphological change and removes the surface Sb2O3 layer, which eliminates the Fermi-level pinning that the oxide layer generates. CuCl2 further enhances the performance due to the passivation of the surface defects, as supported by density functional theory molecular dynamics (DFT-MD) calculations, improving charge separation at the interface. The simple and low-cost semiconductor synthesis method combined with these facile, low-temperature treatments further increases the practical potential of Sb2Se3 for large-scale water splitting.