Migration of halogen vacancies is one of the primary sources of phase segregation and material degradation in lead-halide perovskites. Here we use first principles density functional theory to compare migration energy barriers and paths of bromine vacancies in the bulk and at a (001) surface of cubic CsPbBr₃. Our calculations indicate that surfaces might facilitate bromine vacancy migration in these perovskites, due to their soft structure that allows for bond lengths variations larger than in the bulk. We calculate the migration energy for axial-to-axial bromine vacancy migration at the surface to be only half of the value in the bulk. Furthermore, we study the effect of modifying the surface with four different alkali halide monolayers, finding an increase of the migration barrier to almost the bulk value for the NaCl-passivated system. Migration energies are found to be correlated to the lattice mismatch between the CsPbBr₃ surface and the alkali halide monolayer. Our calculations suggest that surfaces might play a significant role in mediating vacancy migration in halide perovskites, a result with relevance for perovskite nanocrystals with large surface-to-volume ratios. Moreover, we propose viable ways for suppressing this undesirable process through passivation with alkali halide salts.

卤素空位的迁移是卤化铅钙钛矿相分离和材料降解的主要来源之一。在这里，我们使用第一性原理密度泛函理论来比较迁移能垒和溴空位在体块中和立方 CsPbBr ₃的（001）表面的路径. 我们的计算表明，表面可能促进这些钙钛矿中的溴空位迁移，因为它们的软结构允许键长变化大于块体。我们计算出表面轴向到轴向溴空位迁移的迁移能量仅为本体值的一半。此外，我们研究了用四种不同的碱金属卤化物单层改性表面的效果，发现迁移势垒增加到几乎 NaCl 钝化系统的整体值。发现迁移能量与 CsPbBr ₃之间的晶格失配相关表面和碱金属卤化物单层。我们的计算表明，表面可能在介导卤化物钙钛矿中的空位迁移方面发挥重要作用，这一结果与具有大表面积与体积比的钙钛矿纳米晶体相关。此外，我们提出了通过用碱金属卤化物盐钝化来抑制这种不良过程的可行方法。