Screening Mixed-Metal Sn₂M(III)Ch₂X₃ Chalcohalides for Photovoltaic Applications

High Resolution Image Download MS PowerPoint Slide Quaternary mixed-metal chalcohalides (Sn 2 M(III)Ch 2 X 3 ) are emerging as promising lead-free, perovskite-inspired photovoltaic absorbers. Motivated by recent developments of a first Sn 2 SbS 2 I 3 -based device, we used density functional theory to identify lead-free Sn 2 M(III)Ch 2 X 3 materials that are structurally and energetically stable within Cmcm, Cmc 2 1, and P 2 1 / c space groups and have a band gap in the range of 0.7–2.0 eV to cover outdoor and indoor photovoltaic applications. A total of 27 Sn 2 M(III)Ch 2 X 3 materials were studied, including Sb, Bi, and In for the M(III)-site, S, Se, and Te for the Ch-site, and Cl, Br, and I for the X-site. We identified 12 materials with a direct band gap that meet our requirements, namely, Sn 2 InS 2 Br 3, Sn 2 InS 2 I 3, Sn 2 InSe 2 Cl 3, Sn 2 InSe 2 Br 3, Sn 2 InTe 2 Br 3, Sn 2 InTe 2 Cl 3, Sn 2 SbS 2 I 3, Sn 2 SbSe 2 Cl 3, Sn 2 SbSe 2 I 3, Sn 2 SbTe 2 Cl 3, Sn 2 BiS 2 I 3, and Sn 2 BiTe 2 Cl 3 . A database scan reveals that 9 of 12 are new compositions. For all 27 materials, P 2 1 / c is the thermodynamically preferred structure, followed by Cmc 2 1 . In Cmcm and Cmc 2 1, mainly direct gaps occur, whereas indirect gaps occur in P 2 1 / c . To open up the possibility of band gap tuning in the future, we identified 12 promising Sn 2 M(III) 1– a M(III)′ a Ch 2– b Ch′ b X 3– c X′ c alloys, which fulfill our requirements, and an additional 69 materials by combining direct and indirect band gap compounds.