Band-structure, optical properties, and defect physics of the photovoltaic semiconductor SnS

SnS is a potential earth-abundant photovoltaic (PV) material. Employing both theory and experiment to assess the PV relevant properties of SnS, we clarify on whether SnS has an indirect or direct band gap and what is the minority carrier effective mass as a function of the film orientation. SnS has a 1.07 eV indirect band gap with an effective absorption onset located 0.4 eV higher. The effective mass of minority carrier ranges from 0.5 m₀ perpendicular to the van der Waals layers to 0.2 m₀ into the van der Waals layers. The positive characteristics of SnS feature a desirable p-type carrier concentration due to the easy formation of acceptor-like intrinsic Sn vacancy defects. Potentially detrimental deep levels due to Sn_S antisite or S vacancy defects can be suppressed by suitable adjustment of the growth condition towards S-rich.