Promising photovoltaic and solid-state-lighting materials: two-dimensional Ruddlesden–Popper type lead-free halide double perovskites Csn+1Inn/2Sbn/2I3n+1(n= 3) and Csn+1Inn/2Sbn/2Cl3n+1/Csm+1Cum/2Bim/2Cl3m+1(n= 3,m= 1)

Promising 2D Cs₄In_3/2Sb_3/2I₁₀and Cs₄In_3/2Sb_3/2Cl₁₀/Cs₂Cu_1/2Bi_1/2Cl₄lead-free halide double perovskites have suitable direct bandgaps, and ultrahigh optical absorption and carrier mobility.