First-Principles Studies of Band Gap Reductions via Substitutional Defects in Cs2AgBiBr6

ORAL

Abstract

Pb-based halide perovskites have emerged as a promising class of materials for photovoltaic applications, but are undesirable due to their toxicity and instability towards water. Halide double perovskites afford the opportunity for heterovalent substitutions on the metal site and in particular Cs2AgBiBr6 has been found to host a comparably small, if indirect, band gap [1]. Recent studies show that dilute amounts of Tl can further decrease the band gap and moreover, become direct due to the symmetry of the bands [2]. Here we use first-principles calculations to study how substitution of other, non-toxic heavy elements affects the band structure of Cs2AgBiBr6 with the aim of achieving a smaller, direct band gap. Accurately capturing the effect of including heavy elements in a complex, quaternary system requires using large supercells, examining the local structure of substitutional defects, and particular attention must be paid on how to interpret band gap trends calculated with DFT. We explore the possibility of using a semi-empirical approach based on GW quasiparticle corrections to predict band gap trends for dilute defect concentrations. [1] A.H. Slavney et al, J. Am. Chem. Soc., 2016, 138 (7), 2138–2141 [2] A.H. Slavney et al, J. Am. Chem. Soc., 2017, 139 (14), 5015–5018

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Presenters

  • Stephanie Mack

    Physics, Univ of California - Berkeley

Authors

  • Stephanie Mack

    Physics, Univ of California - Berkeley

  • Linn Leppert

    Institute of Physics, University of Bayreuth, Physics, University of Bayreuth

  • Kurt Lindquist

    Chemistry, Stanford University

  • Hemamala Karunadasa

    Chemistry, Stanford University

  • Jeffrey Neaton

    Molecular Foundry, Lawrence Berkeley National Laboratory; Department of Physics, University of California, Berkeley; Kavli Energy Nanosciences Institute at Berkeley, Physics, University of California, Berkeley; Lawrence Berkeley National Laboratory, Department of Physics, University of California, Univ of California - Berkeley, Lawrence Berkeley Natl Lab, Materials Science Division, Lawrence Berkeley National Laboratory, Molecular Foundry, Lawrence Berkeley National Lab, Physics, University of California, Berkeley, Department of Physics UCB; Molecular Foundry LBNL; Kavli ENSI, Lawrence Berkeley National Laboratory, Department of Physics, Univ of California - Berkeley, Lawrence Berkeley National Lab and University of California - Berkeley