Synthesis of AgBiS2 films by sulfurizing Bi/Ag stacks for thin film photovoltaics

Abstract

Silver bismuth sulfide (AgBiS2), comprising non-toxic and naturally abundant elements, has attracted significant attention as a material for solar cells. In this study, we prepared AgBiS2 thin films via a two-stage process of thermal evaporation of Bi/Ag metal film stacks followed by sulfurization at 300–450 °C for 30 min. The structural, microstructural, elemental, optical, and electrical properties of the films were investigated as functions of the sulfurization temperature (TS). X-ray diffraction analysis revealed the formation of the Bi2S3 secondary phase at 300 °C and single-phase AgBiS2 with a cubic structure at 350–450 °C, showing an increase in the crystallite size as the TS increased. Compositional analysis indicated improved stoichiometry of the films with increasing TS from 300 to 450 °C. X-ray photoelectron spectroscopy determined the chemical state of Ag, Bi, and S to be +1, +3, and −2, respectively. Microstructural analysis revealed an improvement in grain size and film uniformity as TS increased from 300 to 450 °C. Optical absorption studies demonstrated an increased bandgap of the AgBiS2 films with increasing TS, from 1.0 eV to 1.05 eV. Electrical measurements revealed p-type conductivity for all the AgBiS2 films. AgBiS2-based thin film solar cells, fabricated from the absorber prepared at TS= 400 °C, exhibited an open-circuit voltage (VOC) of 96.53 mV, short-circuit current density (JSC) of 4.68 mA/cm2, fill factor (FF) of 26%, and an efficiency of 0.13%, indicating a promising potential of AgBiS2 films in thin-film solar cells.