Post-Synthetic Silver Ion and Sulfurization Treatment for Enhanced Performance in Sb$_2$Se$_3$ Water Splitting Photocathodes

Abstract

In the past decade, antimony selenide (Sb$_2$Se$_3$) has made significant progress as a solar energy conversion material. However, the photovoltage deficit continues to pose a challenge and is a major hurdle that must be overcome to reach its maximum solar conversion efficiency. In this study, various post-synthetic treatments are employed, of which the combination of a solution phase silver nitrate treatment and sulfurization has shown to be the most effective approach to mitigate the photovoltage deficit in this Sb$_2$Se$_3$-based device. A significant enhancement in the photovoltage is observed after the treatments, as evident by the increase in the onset potential from 0.18 to 0.40 V versus reversible hydrogen electrode. Multiwavelength Raman shows that combining these two treatments removes amorphous Se and metallic Sb from the surface and yields a high-quality surface layer of Sb$_2$(S$_{1−x}$, Se$_x$)$_3$ on the bulk Sb$_2$Se$_3$ photoabsorber layer. X-ray photoelectron spectroscopy with depth profiling reveals extensive incorporation of silver into the film. Density functional theory calculations suggest that silver ions can intercalate between the [Sb$_4$Se$_6$]$_n$ ribbons and remain in the Ag$^+$ state. This effective treatment combination brings the practicality of the Sb$_2$Se$_3$ photocathode for water splitting one step closer to large-scale applications.