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.
Competing Interests: There are no conflicts to declare.
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