Computational exploration of alternative mixed-valence double perovskites via cation-anion dual-doping strategy

Mixed-valence (Cs2AuAuX6)-Au-I-X-III (X = I, Br, Cl) double perovskites (DPs) exhibit high chemical stability and tunable optical band gaps, which renders their potential for photovoltaics. As an alternative, the suitability of novel mixed-valence mixed-halide perovskites for solar cell devices is studied herein. The cation-anion dual-doping strategy is utilized for (Cs2AuAuX6)-Au-I-X-III, where the Au-I cations are substituted by the Ag-I cations and the anions are doped by different proportions of halide anions. The class of mixed-valence mixed-halide perovskites (Cs2AgAuX4Y2)-Au-I-X-III and (Cs2AgAuX2Y4)-Au-I-X-III (X = I or Br; X = Br or Cl) is comprehensively investigated with regard to their optoelectronic properties and structural stability. Apart from good thermodynamic and mechanical stability, (Cs2AgAuI4X2)-Au-I-I-III (X = Br, Cl) and (Cs2AgAuBr4Cl2)-Au-I-Br-III exhibit optimum band gaps within 1.2-1.4 eV and have low reduced effective masses (<0.25 m(0)) and small exciton binding energies (<110 meV). Additionally, three alternative mixed-halide DPs show high visible-light absorption. Ultimately, the simulated maximum efficiency is within 29-31 % for three novel mixed-halide DPs. Considering structural stability and optoelectronic properties, (Cs2AgAuI4Br2)-Au-I-I-III is expected to be an appropriate candidate for high-efficiency thin-film solar cells. The theoretical prediction of mixed-valence mixed-halide DPs can provide an attractive route to discover high-performance photovoltaic materials.