Computational Screening of 2D All‐Inorganic Lead‐Free Halide Perovskites A3B2X9 for Photovoltaic and Photocatalytic Applications

Abstract Exploration of low‐dimensional Pb‐free halide perovskites with high stability and outstanding properties is still a pursuing target for developing integrated optoelectronic devices. Herein, comprehensive computational screening of a new class of two‐dimensional (2D) all‐inorganic Pb‐free A 3 B 2 X 9 perovskites is performed based on the first‐principles calculations. The results indicate that the structural and electronic properties of 2D A 3 B 2 X 9 structures strongly depend on the B‐X bonding interactions, which makes that their thermodynamic stability follows the trend of A 3 Bi 2 X 9 ≈A 3 Sb 2 X 9 >A 3 In 2 X 9 >A 3 Ga 2 X 9 and their interlayer interactions show a reversal trend. Owing to the lack of lone‐pair electron effect, A 3 In 2 X 9 indicate direct bandgap characteristics and present the relatively smaller bandgaps and higher electron mobilities than A 3 Sb 2 X 9 and A 3 Bi 2 X 9 . Benefit from optimal bandgaps (0.8–2.1 eV) and large absorption coefficients (10 4 –10 5 cm −1 ) in the visible region, A 3 B 2 I 9 (B = In, Sb, Bi) exhibit high power conversion efficiency up to 18.2%. Moreover, A 3 B 2 I 9 (B = Sb, Bi) is verified as efficient photocatalysts for overall water splitting. The theoretical solar‐to‐hydrogen efficiency of Rb 3 Bi 2 I 9 and Cs 3 Bi 2 I 9 are >16%. This work suggests huge potential of 2D A 3 B 2 X 9 perovskites for photovoltaic and photocatalytic applications.