Screening Mixed-Metal Sn2M(III)Ch2X3 Chalcohalides for Photovoltaic Applications
Abstract
Quaternary mixed-metal chalcohalides (Sn2BCh2X3) are emerging as promising lead-free perovskite-inspired photovoltaic absorbers. Motivated by recent developments of a first Sn2BCh2X3-based device, we used density functional theory to identify lead-free Sn2BCh2X3 materials that are structurally and energetically stable within Cmcm, Cmc21 and P21/c space groups and have a band gap in the range of 0.7 to 2.0 eV to cover out- and indoor photovoltaic applications. A total of 27 Sn2BCh2X3 materials were studied, including Sb, Bi, In for B-site, S, Se, Te for Ch-site and Cl, Br, I for X-site. We identified 12 materials with a direct band gap that meet our requirements, namely: Sn2InS2Br3, Sn2InS2I3, Sn2InSe2Cl3, Sn2InSe2Br3, Sn2InTe2Br3, Sn2InTe2Cl3, Sn2SbS2I3, Sn2SbSe2Cl3, Sn2SbSe2I3, Sn2SbTe2Cl3, Sn2BiS2I3 and Sn2BiTe2Cl3. A database scan reveals that 9 out of 12 are new compositions. For all 27 materials, P21/c is the thermodynamically preferred structure, followed by Cmc21. In Cmcm and Cmc21 mainly direct gaps occur, whereas mostly indirects in P21/c. To open up the possibility of band gap tuning in the future, we identified 12 promising Sn2B1-aB'aCh2-bCh'bX3-cXc alloys which fulfill our requirements and additional 69 materials by combining direct and indirect band gap compounds.
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