Chen Yan-Jin, Hou Chunju, Yang Yi
College of Rare Earths and Faculty of Materials, Metallurgy and Chemistry, JiangXi University of Science and Technology, Ganzhou, 341000, China.
School of Science, JiangXi University of Science and Technology, Ganzhou, 341000, China.
Phys Chem Chem Phys. 2023 Apr 12;25(15):10583-10590. doi: 10.1039/d2cp04183a.
Lead halide perovskites have been widely studied in the fields of photovoltaics and optoelectronics for over a decade. The toxicity of lead poses a big challenge to the potential applications of the materials. In recent years, lead-free halide perovskites have received significant attention due to their excellent optoelectronic properties and environment-friendly character. Tin halide perovskites have emerged as one of the most promising candidates for lead-free optoelectronic materials. It is of fundamental importance to understand the surface properties of tin halide perovskites that remain largely unknown. Using the density functional theory (DFT) method, we explore the surface energy and surface stability of low-index surfaces of cubic CsSnX (X = Cl, Br, I), , (100), (110), and (111) surfaces. We calculate the stability phase diagrams of these surfaces and find that the (100) surface is more stable than the (110) and (111) surfaces. Interestingly, Br-terminated (110) and CsBr-terminated (111) polar surfaces are relatively more stable in CsSnBr than those in CsPbBr due to a higher level of valence band maximum and thus lesser energy cost in removing electrons to compensate for the polarity of the former. We calculate the surface energies of CsSnX surfaces that are difficult to access from experiments. The surface energies are very low in comparison with that of oxide perovskites. The origin of this lies in the relatively low binding strength of halide perovskites because of the soft nature of their structures. Furthermore, the connection between exfoliation energy and the cleavage energy in CsSnX is discussed.
十多年来，卤化铅钙钛矿在光伏和光电子领域得到了广泛研究。铅的毒性对这些材料的潜在应用构成了巨大挑战。近年来，无铅卤化钙钛矿因其优异的光电性能和环境友好特性而受到广泛关注。卤化锡钙钛矿已成为无铅光电子材料中最有前途的候选材料之一。了解卤化锡钙钛矿的表面性质至关重要，但目前这些性质在很大程度上仍不为人知。我们使用密度泛函理论（DFT）方法，研究了立方CsSnX（X = Cl、Br、I）低指数表面（100）、（110）和（111）的表面能和表面稳定性。我们计算了这些表面的稳定相图，发现（100）表面比（110）和（111）表面更稳定。有趣的是，Br端接的（110）和CsBr端接的（111）极性表面在CsSnBr中比在CsPbBr中相对更稳定，这是因为前者的价带最大值更高，因此去除电子以补偿极性的能量成本更低。我们计算了实验中难以获得的CsSnX表面的表面能。与氧化物钙钛矿相比，这些表面能非常低。其原因在于卤化物钙钛矿结构的软性导致其结合强度相对较低。此外，还讨论了CsSnX中剥离能与解理能之间的关系。
