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 Cs2AgBiX6 and 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 Cs2AgBiX6 motif.
Bibliographical noteFunding Information:
The work presented in this Letter was performed on the ARCHER UK National Supercomputing Service, via our membership of the UK’s HEC Materials Chemistry Consortium, funded by EPSRC (EP/L000202). C.N.S. is grateful to the Department of Chemistry at UCL for the provision of a DTA studentship. D.O.S. acknowledges support from the SUPERSOLAR Solar Energy Hub (EP/J017361/1) and EP/ N01572X/1. The work at Bath was supported by the ERC (Grant No. 277757) and the EPSRC (Grant No. EP/K016288/ 1, EP/L017792/1, and EP/M009580/1). A.W. and D.O.S. acknowledge membership of the Materials Design Network.
© 2016 American Chemical Society.