Department of Chemistry, University of Cologne, Luxemburger Straße 116, 50939 Cologne Germany.
Sci Rep. 2017 Jan 13;7:40267. doi: 10.1038/srep40267.
We present investigations on the interface formation between the hybrid perovskite MAPbI and various substrates, covering a wide range of work functions. The perovskite films are incrementally evaporated in situ while the electronic structure is evaluated using photoelectron spectroscopy. Our results show that there is an induction period in the growth of the perovskite during which volatile compounds are formed, catalyzed by the substrate. The duration of the induction period depends strongly on the nature of the substrate material, and it can take up to 20-30 nm of formal precursor deposition before the surface is passivated and the perovskite film starts forming. The stoichiometry of the 2-3 nm thin passivation layer deviates from the expected perovskite stoichiometry, being rich in decomposition products of the organic cation. During the regular growth of the perovskite, our measurements show a deviation from the commonly assumed flat band condition, i.e., dipole formation and band bending dominate the interface. Overall, the nature of the substrate not only changes the energetic alignment of the perovskite, it can introduce gap states and influence the film formation and morphology. The possible impact on device performance is discussed.
我们对混合钙钛矿 MAPbI 与各种功函数的衬底之间的界面形成进行了研究。在原位逐渐蒸镀钙钛矿的同时，使用光电子能谱评估其电子结构。结果表明，钙钛矿在生长过程中有一个诱导期，在此期间，在衬底的催化作用下形成挥发性化合物。诱导期的持续时间强烈依赖于衬底材料的性质，在表面钝化和钙钛矿薄膜开始形成之前，可能需要 20-30nm 的前体沉积。2-3nm 厚的钝化层的化学计量比偏离了预期的钙钛矿化学计量比，其富含有机阳离子的分解产物。在钙钛矿的正常生长过程中，我们的测量结果表明偏离了通常假设的平带条件，即偶极子形成和能带弯曲主导了界面。总的来说，衬底的性质不仅改变了钙钛矿的能级排列，还会引入带隙态并影响薄膜的形成和形貌。讨论了对器件性能的可能影响。
