Solution-processed Sb 2 Se 3 photocathodes under Se-rich conditions and their photoelectrochemical properties.

In this study, selenium (Se)-rich antimony selenide (Sb 2 Se 3 ) films were fabricated by applying a solution process with the solvents ethylenediamine and 2-mercaptoethanol to optimize the photoelectrochemical (PEC) performance of the Sb 2 Se 3 photocathode. Various antimony (Sb)-Se precursor solutions with different molar ratios of Sb and Se (Sb : Se = 1 : 1.5, 1 : 3, 1 : 4.5, 1 : 7.5, and 1 : 9) were prepared to attain Se-rich fabrication conditions. As a result, the Se-rich Sb 2 Se 3 films fabricated using the Sb-Se precursor solution with a molar ratio of Sb : Se = 1 : 7.5 exhibited an improved PEC performance, compared to the stoichiometric Sb 2 Se 3 film. The charge transport was improved by the abundant Se element and thin selenium oxide (Se 2 O 3 ) layer in the Se-rich Sb 2 Se 3 film, resulting in a decrease in Se vacancies and substitutional defects. Moreover, the light utilization in the long wavelength region above 800 nm was enhanced by the light-trapping effect because of the nanowire structure in the Se-rich Sb 2 Se 3 film. Hence, the optimal Se-rich Sb 2 Se 3 photocathodes showed an improved photocurrent density of -0.24 mA cm -2 at the hydrogen evolution reaction potential that was three times higher than that of the stoichiometric Sb 2 Se 3 photocathodes (-0.08 mA cm -2 ).