Tin Sulfide/Gallium Oxide Heterojunctions for Solar Water Splitting

Tin (II) sulfide (SnS) is a promising semiconductor material for next‐generation solar energy conversion due to its favorable bandgap, elemental abundance, low toxicity, and low cost. A major challenge, however, lie in the low open circuit voltages that are typically obtained in SnS‐based devices. Herein, a low‐cost solution‐phase deposition technique is used to prepare SnS thin films and investigate different junction materials (Ga 2 O 3 and In 2 S 3 ) to improve the photovoltage in SnS‐based water splitting photocathodes. Molecular inks are prepared by dissolving SnS powder in solvent mixtures of ethylenediamine and 1,2‐ethanedithiol. SnS thin films are then successfully deposited by spin coating the inks onto substrates, followed by a heat treatment at 350°C in an inert atmosphere. With a photoelectrode based on a SnS/Ga 2 O 3 heterojunction, an onset potential of +0.25 V versus reversible hydrogen electrode (RHE) is achieved for photoelectrochemical hydrogen evolution in pH 7 phosphate buffer, which is until now the earliest onset potential (highest photovoltage) among nontoxic replacements to CdS junctions in SnS‐based water splitting systems.