Research on organic-inorganic lead halide perovskite solar cells (PSCs) has developed rapidly in the last decade, with energy conversion efficiency (PCE) increasing from 3.8% in 2009 to 25.7% in 2022, [1][2][3] which is an unprecedented rate of development in the photovoltaic (PV) field. Owing to the superior properties of perovskite materials, such as suitable and tunable bandgap, long carrier diffusion length and lifetime, high optical absorption coefficient, high charge carrier mobility, and simple solution processing, PSCs have the potential to compete with the traditional crystalline silicon, CdTe, and organic solar cells in terms of both performance and cost. [2,4,5] Unfortunately, there are still two unresolved issues on the road to the actual commercialization of PSCs: one is the toxicity due to the presence of lead ions, and the other is the intrinsic instability due to the volatility of the organic components. [2,[6][7][8] To overcome the intrinsic instability of perovskite, an intuitive and valid approach is replacing the A-site organic cation (e.g., MA þ and FA þ ) in the traditional organic-inorganic perovskite ABX 3 with an inorganic cation (e.g., Cs þ ), which can increase the decomposition energy of perovskite and thus enhance the intrinsic stability. [9] To address the toxicity issue, the intuitive solution strategy is the substitution of Pb 2þ with divalent nontoxic metal ions (e.g., Sn 2þ and Ge 2þ ). [10][11][12] However, since Sn 2þ and Ge 2þ occupy high-energy 5s and 4s orbitals, they are easily oxidized in the air to form Sn 4þ and Ge 4þ . [13] Another strategy employs trivalent nontoxic metal ions (e.g., Bi 3þ and Sb 3þ ) to replace Pb 2þ , forming 0D or 2D layered perovskites with the formula Cs 3 M 2 X 9 (M = Bi 3þ , Sb 3þ ; X = I À , Br À , Cl À ). [14][15][16][17][18] Due to the isolated network of metal-halide octahedral units, these materials show undesirable optoelectronic properties, such as low carrier mobilities and indirect bandgaps. [17,18] Recently, a promising novel strategy has been proposed by replacing the B-site ions in the adjacent lattice of the traditional perovskite structure ABX 3 with a pair of heterovalent (i.e., monovalent and trivalent) nontoxic metal ions to form the double perovskite structure with the formula A