Photoelectrochemical performances of the cubic AgSnSe₂ thin film electrodes created using the selenization of thermal evaporated Ag-Sn metal precursors

In this study, we prepared the cubic AgSnSe₂ thin film photoelectrodes on substrates using the selenization of Ag–Sn metal precursors and examined the influence of silver content in samples on their photoelectrochemical properties in the aqueous solution. With the selenization temperature kept at 410 °C for 1 h in the selenization apparatus, the cubic AgSnSe₂ samples can be obtained. The results of phase characterization show that the phase change from the cubic AgSnSe₂ to the cubic Ag₈SnSe₆ phase takes place at the selenization temperature between 425 to 440 °C. The optical energy band gaps, carrier concentrations, and mobilities of samples are in the range of 1.24–1.30 eV, 1.75 × 10¹⁸–4.68 × 10¹⁹ cm⁻³, and 43–253 cm²/V/s, respectively. It was found that the sample with the [Ag]/[Ag + Sn] molar ratio of 0.48 had a maximum photo-enhancement current density of 1.26 mA/cm² at an external bias of + 1.23 V vs. the reverse hydrogen electrode in the 0.35 M Na₂S + 0.25 M K₂SO₃ aqueous solution. The electrochemical impedance spectra of samples in the aqueous solution containing S²⁻ and SO₃ ²⁻ ions were also employed to examine the possible reaction mechanisms taking place at the sample surfaces.