Defect chemistry for extrinsic doping in ductile semiconductor α-Ag2S

As a new type of inorganic ductile semiconductor, silver sulfide (α-Ag₂S) has garnered a plethora of interests in recent years due to its promising applications in flexible electronics. However, the lack of detailed defect calculations and chemical intuition has largely hindered the optimization of material's performance. In this study, we systematically investigate the defect chemistry of extrinsic doping in α-Ag₂S using first-principles calculations. We computationally examine a broad suite of 17 dopants and find that all aliovalent elements have extremely low doping limits (<0.002%) in α-Ag₂S, rendering them ineffective in tuning the electron concentrations. In contrast, the isovalent elements Se and Te have relatively high doping limits, being consistent with the experimental observations. While the dopant Se or Te itself does not provide additional electrons, its introduction has a significant impact on the band gap, the band-edge position, and especially the formation energy of Ag interstitials, which effectively improve the electron concentrations by 2–3 orders of magnitudes. The size effects of Se and Te doping are responsible for the more favorable Ag interstitials in Ag₂S_0.875Se_0.125 and Ag₂S_0.875Te_0.125 with respect to pristine Ag₂S. This work serves as a theoretical foundation for the rational design of Ag₂S-based functional materials.