title: Can Pb-Free Halide Double Perovskites Support High-Efficiency Solar Cells?
abstract: The methylammonium lead halides have become champion photoactive semiconductors for solar cell applications; however, issues still remain with respect to chemical instability and potential toxicity. Recently, the Cs2AgBiX6(X = Cl, Br) double perovskite family has been synthesized and investigated as stable nontoxic replacements. We probe the chemical bonding, physical properties, and cation anti-site disorder of Cs2AgBiX6and related compounds from first-principles. We demonstrate that the combination of Ag(I) and Bi(III) leads to the wide indirect band gaps with large carrier effective masses owing to a mismatch in angular momentum of the frontier atomic orbitals. The spectroscopically limited photovoltaic conversion efficiency is less than 10% for X = Cl or Br. This limitation can be overcome by replacing Ag with In or Tl; however, the resulting compounds are predicted to be unstable thermodynamically. The search for nontoxic bismuth perovskites must expand beyond the Cs2AgBiX6motif.
authors.affiliation: Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London , 20 Gordon Street, London WC1H 0AJ, United Kingdom.
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Savory
authors.affiliation: Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom; Global E3 Institute and Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, South Korea.
authors.forename: Aron
authors.initials: A
authors.lastname: Walsh
authors.affiliation: Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom; Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom.
authors.forename: David O
authors.initials: DO
authors.lastname: Scanlon