Chalcogenide Perovskites (ABS₃; A = Ba, Ca, Sr; B = Hf, Sn): An Emerging Class of Semiconductors for Optoelectronics

Chalcogenide perovskites have received considerable interest in the photovoltaic research community because of their stability, nontoxicity, and lead-free composition. However, because of the huge computational cost, theoretical study focusing on excitonic and polaronic properties is not explored rigorously. Herein, we capture the excitonic and polaronic effects in a series of chalcogenide perovskites ABS₃, where A = Ba, Ca, Sr and B = Hf, Sn, by employing state-of-the-art hybrid density functional theory and many-body perturbative approaches, viz., GW and BSE. We find that they possess an exciton binding energy larger than that of 3D inorganic-organic hybrid perovskites. We examine the interplay of electronic and ionic contributions to the dielectric screening and conclude that the electronic contribution is dominant over the ionic contribution. Using the Feynman polaron model, polaron parameters are computed, and charge-separated polaronic states are less stable than bound excitons. Finally, the theoretically calculated spectroscopic limited maximum efficiency suggests that among all chalcogenide perovskites, CaSnS₃ could serve as the best choice for photovoltaic applications.