Solution phase treatments of Sb 2 Se 3 heterojunction photocathodes for improved water splitting performance.

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 O 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.