Photoelectrochemical performances of kesterite Ag₂ZnSnSe₄ photoelectrodes in the salt-water and water solutions

In this study, we prepare quaternary silver-zinc-tin-selenide samples on various substrates using the selenization of thermally evaporated silver-zinc-tin metal precursors. The [Zn]/[Sn] molar ratio in metal precursors is verified to study its influence on the structural, optical and photoelectrochemical properties of the Ag-Zn-Sn-Se samples in various electrolytes. After various selenization tests, a selenization process with the temperature of 410 °C and time of 90 min is employed for the preparation of quaternary Ag-Zn-Sn-Se samples. X-ray diffraction patterns and Raman spectra of samples show that the crystal phases of samples change from the cubic AgSnSe₂/kesterite Ag₂ZnSnSe₄ mixing phases, the kesterite Ag₂ZnSnSe₄ phase to the kesterite Ag₂ZnSnSe₄/cubic ZnSe mixing phases with an increase in the [Zn]/[Sn] molar ratio in the metal precursors. Direct energy band gaps of samples locate in the range of 1.30–1.34 eV. Carrier concentration and mobility of samples are in the ranges of 8.99 × 10¹⁵–5.97 × 10¹⁸ cm⁻³ and 7.72–76.08 cm²/V s, respectively. The sample with the [Zn]/[Sn] molar ratio of 1.42 has the maximum photo-enhancement current density of 5.69 and 11.12 mA/cm² at an applied bias of +1.0 V vs. an Ag/AgCl electrode in the 0.5 M K₂SO₄ and 1 M NaCl aqueous solution, respectively.