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 A₃B₂X₉ perovskites is performed based on the first-principles calculations. The results indicate that the structural and electronic properties of 2D A₃B₂X₉ structures strongly depend on the B-X bonding interactions, which makes that their thermodynamic stability follows the trend of A₃Bi₂X₉≈A₃Sb₂X₉>A₃In₂X₉>A₃Ga₂X₉ and their interlayer interactions show a reversal trend. Owing to the lack of lone-pair electron effect, A₃In₂X₉ indicate direct bandgap characteristics and present the relatively smaller bandgaps and higher electron mobilities than A₃Sb₂X₉ and A₃Bi₂X₉. Benefit from optimal bandgaps (0.8–2.1 eV) and large absorption coefficients (10⁴–10⁵ cm⁻¹) in the visible region, A₃B₂I₉ (B = In, Sb, Bi) exhibit high power conversion efficiency up to 18.2%. Moreover, A₃B₂I₉ (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 A₃B₂X₉ perovskites for photovoltaic and photocatalytic applications.

中文翻译：

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用于光伏和光催化应用的二维全无机无铅卤化物钙钛矿 A3B2X9 的计算筛选

探索具有高稳定性和优异性能的低维无铅卤化物钙钛矿仍然是开发集成光电器件的追求目标。在此，基于第一原理计算对一类新型二维（2D）全无机无铅A ₃ B ₂ X _{9钙钛矿进行了全面的计算筛选。}结果表明，2D A ₃ B ₂ X ₉结构的结构和电子性质强烈依赖于BX键合相互作用，这使得它们的热力学稳定性遵循A ₃ Bi ₂ X ₉ ≈A ₃ Sb ₂ X ₉ > A ₃ In ₂ X ₉ >A ₃ Ga ₂ X ₉及其层间相互作用呈现反转趋势。由于缺乏孤对电子效应，A ₃ In ₂ X _{9表现出直接带隙特性，并且比A 3} Sb ₂ X ₉和A ₃ Bi ₂ X ₉具有相对更小的带隙和更高的电子迁移率。受益于可见光区域的最佳带隙 (0.8–2.1 eV) 和大吸收系数 (10 ⁴ –10 ⁵ cm ^{-1 )，A} ₃ B ₂ I ₉ (B = In, Sb, Bi) 表现出高功率转换效率至 18.2%。此外，A ₃ B ₂ I ₉ (B = Sb, Bi) 被验证为整体水分解的有效光催化剂。_{Rb 3} Bi ₂ I ₉和Cs ₃ Bi ₂ I ₉的理论太阳能-氢气效率>16%。这项工作表明 2D A ₃ B ₂ X ₉钙钛矿在光伏和光催化应用方面具有巨大潜力。