论文标题
缺陷对PBI2的工作函数和能量比对的影响：对太阳能电池应用的影响
Effects of Defect on Work Function and Energy Alignment of PbI2: Implications for Solar Cell Applications
论文作者
论文摘要
二维（2D）层状碘化铅（PBI2）是在二甲基铅钙钛矿的合成过程中的重要前体和常见的残留物质。目前存在一些关于过量PBI2对太阳能电池对其能量比对的效率和稳定性的影响和稳定性的辩论和不确定性。在此，通过应用第一原理计算，我们研究了与单层PBI2（ML-PBI2）的碘空位（VI）和间质碘（II）缺陷相关的能量，工作函数的变化以及与碘空位（VI）和间质碘（II）缺陷相关的缺陷水平。我们发现，PBI2的形成能的VI非常低，为0.77和0.19 eV，分别用于稀释和高浓度，反映了孤立的VI的合并趋势，远低于其他2D材料（如磷烯）的空缺。与VI相似，发现低层II为0.65 eV，这意味着这种缺陷量很高。这两种缺陷都产生了间隙缺陷水平，这主要是由于暴露的Pb或插入的P轨道的不饱和化学键。这种富有缺陷的水平允许VI和II作为PBI2中电子/孔载体的储层或水槽。 Our results suggest that the remnant PbI2 in perovskite MAPbI3 (or FAPbI3) would play dual opposite roles in affecting the efficiency of the perovskite: (1) Forming Schottky-type interface with MAPbI3 (or FAPbI3) in which the built-in potential would facilitate the electron-hole separation and prolong the carrier lifetime; （2）由于深度有缺陷的水平而充当重组中心。为了通过肖特基效应促进效率，我们的工作表明II缺陷受到青睐，并减少重组中心，应抑制VI缺陷。我们的结果将有益于改善相关光电应用的策略。
Two-dimensional (2D) layered lead iodide (PbI2) is an important precursor and common residual species during the synthesis of lead-halide perovskites. There currently exist some debates and uncertainties about the effect of excess PbI2 on the efficiency and stability of the solar cell with respect to its energy alignment and energetics of defects. Herein, by applying the first-principles calculations, we investigate the energetics, changes of work function and the defective levels associated with the iodine vacancy (VI) and interstitial iodine (II) defects of monolayer PbI2 (ML-PbI2). We find that the PbI2 has a very low formation energy of VI of 0.77 and 0.19 eV for dilute and high concentration, respectively, reflecting coalescence tendency of isolated VI, much lower than that of vacancies in other 2D materials like phosphorene. Similar to VI, a low formation energy of II of 0.65 eV is found, implying a high population of such defects. Both defects generate in-gap defective levels which are mainly due to the unsaturated chemical bonds of p-orbitals of exposed Pb or inserted I. Such rich defective levels allow the VI and II as the reservoir or sinks of electron/hole carriers in PbI2. Our results suggest that the remnant PbI2 in perovskite MAPbI3 (or FAPbI3) would play dual opposite roles in affecting the efficiency of the perovskite: (1) Forming Schottky-type interface with MAPbI3 (or FAPbI3) in which the built-in potential would facilitate the electron-hole separation and prolong the carrier lifetime; (2) Acting as the recombination centers due to the deep defective levels. To promote the efficiency by the Schottky effect, our work reveals that the II defect is favored, and to reduce the recombination centers the VI defect should be suppressed. Our results shall be beneficial in improving strategies for the related optoelectronics applications.
