Influences of Silver and Zinc Contents in the Stannite Ag₂ZnSnS₄ Photoelectrodes on Their Photoelectrochemical Performances in the Saltwater Solution

Multicomponent metal sulfide (stannite Ag₂ZnSnS₄) samples were grown onto the conductive metal oxide-coated glass substrates by using the sulfurization of cosputtering silver-zinc-tin precursors. Several [Ag]/[Zn + Sn] and [Zn]/[Sn] ratios were set in the metal precursors to investigate their influences on the crystal phases, microstructures, and physical properties of the stannite Ag₂ZnSnS₄ samples. The results of the crystal phases and the compositions of the samples showed that the stannite Ag₂ZnSnS₄ phase can be obtained using the two-step sulfurization process, which maintained the silver-zinc-tin precursors at 160 °C for 1 h and then kept them at 450 °C for 30 min under a sulfur/nitrogen atmosphere. N-type stannite Ag₂ZnSnS₄ samples with the carrier concentrations of 5.54 × 10¹² to 9.11 × 10¹² cm^-3 can be obtained. High resistivities of Ag₂ZnSnS₄ samples were observed because of the low values of carrier concentration. Increasing the silver content in the sample can improve its photoelectrochemical (PEC) performance because of the decrease in the sample resistivity. The ratio of [Ag]/[Zn + Sn] at 0.8 and the ratio of [Zn]/[Sn] set at 0.90 in the stannite Ag₂ZnSnS₄ sample had the highest PEC performance of 0.31 mA·cm^-2, with the potential set at 1.23 V versus the relative hydrogen electrode applied on the sample because of it having the lowest charge-transfer resistance in the electrolyte.