Two-dimensional (2D) organic–inorganic hybrid iodide perovskites have been put forward in recent years as stable alternatives to their three-dimensional (3D) counterparts. Using first-principles calculations, we demonstrate that equilibrium concentrations of point defects in the 2D perovskites PEA₂PbI₄, BA₂PbI₄, and PEA₂SnI₄ (PEA, phenethylammonium; BA, butylammonium) are much lower than in comparable 3D perovskites. Bonding disruptions by defects are more destructive in 2D than in 3D networks, making defect formation energetically more costly. The stability of 2D Sn iodide perovskites can be further enhanced by alloying with Pb. Should, however, point defects emerge in sizable concentrations as a result of nonequilibrium growth conditions, for instance, then those defects likely hamper the optoelectronic performance of the 2D perovskites, as they introduce deep traps. We suggest that trap levels are responsible for the broad sub-bandgap emission in 2D perovskites observed in experiments.

中文翻译：

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卤化物钙钛矿的缺陷：是否有助于从 3D 转变为 2D？

近年来，二维（2D）有机-无机杂化碘化物钙钛矿被提出作为三维（3D）对应物的稳定替代品。使用第一性原理计算，我们证明 2D 钙钛矿 PEA ₂ PbI ₄、 BA ₂ PbI ₄和 PEA ₂ SnI ₄（PEA，苯乙基铵；BA，丁基铵）中点缺陷的平衡浓度远低于同类 3D 钙钛矿。缺陷造成的键合破坏在 2D 网络中比在 3D 网络中更具破坏性，这使得缺陷形成的成本更高。通过与 Pb 合金化可以进一步增强 2D Sn 碘化物钙钛矿的稳定性。然而，如果由于非平衡生长条件而出现相当大的点缺陷，那么这些缺陷可能会阻碍二维钙钛矿的光电性能，因为它们会引入深陷阱。我们认为陷阱能级是实验中观察到的二维钙钛矿中宽亚带隙发射的原因。