Thermodynamic, electronic and optical properties of lead-free Hybrid double perovskite alloys of MA2B+B3+Br6 (B+=Ag, K, Tl, B3+=Bi, Sb, In)

Abstract

Organic-inorganic lead-free halide double perovskites A 2 B + B 3+ X 6 have attracted attention as potential lead-free perovskite solar cell absorbers in recent years. Here, using MA 2 AgBiBr 6 as the host lattice, we employed first-principles calculations combined with statistical analysis to investigate the thermodynamic stability, electronic and optical properties of MA 2 AgSb x Bi 1-x Br 6 , MA 2 AgIn x Bi 1-x Br 6 , MA 2 K x Ag 1-x BiBr 6 and MA 2 Tl x Ag 1-x BiBr 6 alloys. The phase diagram determined the miscibility gap and critical temperature of these MA 2 AgBiBr 6 -derived double perovskites to be 395 K, 281 K, 391 K, and 417 K, respectively. Meanwhile, the band gap was found to increase with higher concentrations of In and K, whereas it decreased with greater amounts of Sb and Tl. Consequently, a band gap modulation of approximately 0.45 eV was achieved through mixed-metal alloying. Band structure calculations indicate that opposite bandgap shift directions associated with doped substitution arise from different atomic configurations for these atoms. Associated optical properties of the four-metal systems are also assessed. These results indicate that halide double perovskites have great potential for applications in solar cells and luminescent materials.