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

Mixed-valence Cs₂Au^IAu^IIIX₆ (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 Cs₂Au^IAu^IIIX₆, 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 Cs₂Ag^IAu^IIIX₄Y₂ and Cs₂Ag^IAu^IIIX₂Y₄ (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, Cs₂Ag^IAu^IIII₄X₂ (X = Br, Cl) and Cs₂Ag^IAu^IIIBr₄Cl₂ exhibit optimum band gaps within 1.2–1.4 eV and have low reduced effective masses (<0.25 m₀) 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, Cs₂Ag^IAu^IIII₄Br₂ 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.