RESEARCH ARTICLE

Facet-dependent exfoliation feasibility and optoelectronic properties of two-dimensional all-inorganic halide perovskites    

Xiaojie Ren, Yuxin Zhan, Shuai Zhao, Huanhuan Li

2026, 19 (2): 13.https://doi.org/10.2738/foe.2026.0013

Two-dimensional (2D) all-inorganic halide perovskites exhibit promise for optoelectronic applications, yet selective exfoliation along specific crystallographic planes remains a critical challenge for performance optimization. Using first-principles calculations combined with device simulations, we systematically investigated the structural stability, exfoliation feasibility, and optoelectronic properties of 24 all-inorganic 2D perovskites derived from the (100) and (111) planes of cubic perovskites, specifically the A2BX4 and A3B′2X9 series (A = Cs, Rb; B = Pb, Sn; B′ = Bi, Sb; X = Cl, Br, I). Our results demonstrate that (111)-derived A3B′2X9 perovskites exhibit significantly lower exfoliation energies (23.1−62.1 meV/Å2) than (100)-derived A2BX4 counterparts (59.7−174.0 meV/Å2), attributed to weaker van der Waals interlayer coupling in the former. Rb3Bi2I9 possesses an ultralow exfoliation energy of 23.1 meV/Å2, rivaling that of graphene and demonstrating exceptional potential for mechanical exfoliation of high-quality monolayers. A2BX4 monolayers exhibit direct band gaps, which are favorable for optoelectronic applications; whereas A3B′2X9 monolayers display indirect band gaps. Among all investigated materials, monolayer Rb2SnBr4 emerges as an outstanding candidate, featuring an ideal direct band gap of 1.34 eV (HSE06) that perfectly matches the Shockley−Queisser limit for single-junction solar cells. SCAPS-1D device simulations further predict that optimized Rb2SnBr4-based solar cells can achieve a remarkable theoretical power conversion efficiency of 27.10% under defect densities below 1014 cm−3. This work establishes that (111) plane cleavage is optimal for synthesizing exfoliable 2D perovskites, while (100) plane orientation enables superior direct band gap characteristics for photovoltaic applications, providing critical design principles for crystallographic plane engineering in halide perovskite devices.

一、研究背景

三维卤化钙钛矿ABX₃因角共享八面体框架而具有优异光电性能，但光照、湿气和温度波动导致的结构不稳定性是其主要短板。二维（2D）钙钛矿通过引入间隔层能在保留光电性能的同时显著提升稳定性，而剥离能（Eexf）是衡量从3D晶格中分离单层难易程度的关键参数。然而，针对不同晶体学面方向对全无机2D钙钛矿剥离可行性和光电性质影响的系统研究仍十分缺乏。

二、主要内容

本研究采用第一性原理计算结合SCAPS-1D器件模拟，研究了源自立方钙钛矿（100）面和（111）面的24种全无机2D钙钛矿（A₂BX₄和A₃B'₂X₉两大系列）。结果表明，（111）面衍生A₃B'₂X₉的剥离能（23.1−62.1 meV/Ų）显著低于（100）面衍生A₂BX₄（59.7−174.0 meV/Ų），归因于更弱的范德华层间耦合。其中Rb₃Bi₂I₉剥离能仅23.1 meV/Ų，与石墨烯相当，展现出优异的机械剥离潜力。

在电子结构方面，单层A₂BX₄呈直接带隙，有利于光电应用；A₃B'₂X₉则呈间接带隙。HSE06方法获得单层Rb₂SnBr₄的直接带隙为1.34 eV，与单结太阳能电池的Shockley-Queisser极限精确匹配。SCAPS-1D模拟进一步表明，在吸收层厚度约1.2 µm、缺陷密度低于10¹⁴ cm⁻³的优化条件下，Rb₂SnBr₄基器件理论PCE可达27.10%。PCE对缺陷密度极为敏感，当缺陷密度超过10¹⁶ cm⁻³时效率骤降至15%以下。

三、创新点

（1）首次对源自立方钙钛矿（100）和（111）两个晶面的24种全无机2D卤化钙钛矿进行系统性第一性原理剥离能计算，揭示了晶面取向对层间相互作用和剥离可行性的决定性影响，建立了"（111）面有利于剥离、（100）面有利于光电性能"的晶面工程设计准则。

（2）发现Rb₃Bi₂I₉具有23.1 meV/Ų的超低剥离能（与石墨烯相当），为机械剥离高质量全无机钙钛矿单层提供了新的候选材料，拓展了无铅低毒2D钙钛矿的材料库。

（3）预测单层Rb₂SnBr₄具备1.34 eV的理想直接带隙，与单结太阳能电池的Shockley-Queisser极限精确匹配；SCAPS-1D模拟进一步证明，在优化条件下其理论PCE可达27.10%，验证了无铅钙钛矿在高效光伏应用中的可行性。

四、总结与展望

本研究揭示了晶面取向对全无机2D卤化钙钛矿剥离可行性和光电性质的调控规律，建立了"（111）面利于剥离、（100）面利于光电性能"的设计准则。Rb₂SnBr₄凭借理想带隙和27.10%的理论PCE，展现出作为高效无铅光伏材料的重要潜力。未来可在实验层面验证超低剥离能材料的可剥离性并优化单层制备工艺，在理论层面结合机器学习实现更大化学空间的高通量筛选，加速新型2D钙钛矿材料的发现。

 （以上文字包含AI生成内容，仅供参考，请以原文为准。）

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