Title: Modulation of Point Defect Properties Near Surfaces in Metal Halide Perovskites Show Chinese title

Title: 金属卤化物钙钛矿表面附近点缺陷特性的调制

Abstract: It is now widely recognized that surface and interfacial defects exhibit distinct behavior compared to bulk defects in metal halide perovskites. However, the transition from bulk to surface behavior and the spatial extent of the surface's influence are not well understood. To address this, we conducted first-principles calculations on iodine vacancies and interstitial defects in methylammonium lead iodide and cesium lead iodide at various depths from the surface, enabling us to map out depth-dependent behavior. We find that the defect formation energy follows a saturating exponential curve as the defect moves away from the surface to the bulk. Using first-principles calculated defect formation energies, we quantify the extent of the surface's influence by calculating the decay length associated with each defect. The difference between the surface and bulk defect formation energy is found to be as high as 1.12 eV for the negatively charged iodine vacancy in methylammonium lead iodide, leading to the enrichment of the surface with defects. Through analysis of defective structures, we find that the differences in the bulk and surface defect properties are a consequence of different bond lengths and in some cases, even changes in bonding and coordination environments. Finally, we determine how the defect transition levels change as a function of the layer index, which could contribute to increased non-radiative recombination. Our findings pave the way for a systematic treatment of non-radiative losses in perovskite solar cells that incorporate spatially dependent defect densities and transition levels. Show Chinese abstract

Abstract: 现在普遍认为，表面和界面缺陷在金属卤化物钙钛矿中表现出与体缺陷不同的行为。然而，从体缺陷到表面行为的转变以及表面影响的空间范围尚不明确。为了解决这个问题，我们在甲基铵铅碘化物和铯铅碘化物中对不同深度处的碘空位和间隙缺陷进行了第一性原理计算，使我们能够绘制出深度相关的特性。我们发现，随着缺陷远离表面进入体相，缺陷形成能遵循一个饱和指数曲线。利用第一性原理计算的缺陷形成能，我们通过计算与每个缺陷相关的衰减长度来量化表面影响的范围。发现甲基铵铅碘化物中带负电的碘空位的表面和体缺陷形成能之间的差异高达1.12 eV，导致表面缺陷富集。通过分析缺陷结构，我们发现体缺陷和表面缺陷特性的差异是由于不同的键长，有时甚至由于键合和配位环境的变化。最后，我们确定了缺陷过渡能级如何随层索引变化，这可能导致非辐射复合增加。我们的研究结果为系统处理包含空间依赖的缺陷密度和过渡能级的钙钛矿太阳能电池中的非辐射损失铺平了道路。