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

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)approximate to 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 Rb3Bi2I9 and Cs3Bi2I9 are >16%. This work suggests huge potential of 2D A(3)B(2)X(9) perovskites for photovoltaic and photocatalytic applications.