Abstract
Antimony selenide (Sb$_2$Se$_3$) 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 Sb$_2$Se$_3$/TiO$_2$-based photocathodes for photoelectrochemical water splitting were explored to address this challenge. The FTO/Ti/Au/Sb$_2$Se$_3$ (substrate configuration) stack was treated with (NH$_4$)$_2$S as an etching solution, followed by CuCl$_2$ treatment prior to deposition of the TiO$_2$ by atomic layer deposition. The different treatments show different mechanisms of action compared to similar reported treatments of the back Au/Sb$_2$Se$_3$ 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 Sb$_2$Se$_3$ films. From SEM and XPS studies, it is clear that the etching treatment induces a morphological change and removes the surface Sb$_2$Se$_3$ layer, which eliminates the Fermi-level pinning that the oxide layer generates. CuCl$_2$ 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 Sb$_2$Se$_3$ for large-scale water splitting.
Adams, Pardis