Alkhalifah Ghadah, Marshall Angelo D, Rudayni Fatimah, Wanigasekara Shanika, Wu Judy Z, Chan Wai-Lun
Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, United States.
Department of Physics, College of Science, King Faisal University (KFU), Al-Ahsa 31982, Saudi Arabia.
J Phys Chem Lett. 2022 Jul 28;13(29):6711-6720. doi: 10.1021/acs.jpclett.2c01940. Epub 2022 Jul 18.
Halide perovskites intrinsically contain a large amount of point defects. The interaction of these defects with photocarriers, photons, and lattice distortion remains a complex and unresolved issue. We found that for halide perovskite films with excess halide vacancies, the Fermi level can be shifted by as much as 0.7 eV upon light illumination. These defects can trap photocarriers for hours after the light illumination is turned off. The enormous light-induced Fermi level shift and the prolonged electron trapping are explained by the capturing of photocarriers by halide vacancies at the surface of the perovskite film. The formation of this defect-photocarrier complex can result in lattice deformation and an energy shift in the defect state. The whole process is akin to polaron formation at a defect site. Our data also suggest that these trapped carriers increase the electrical polarizability of the lattice, presumably by enhancing the defect migration rate.
卤化物钙钛矿本质上含有大量的点缺陷。这些缺陷与光载流子、光子以及晶格畸变之间的相互作用仍然是一个复杂且尚未解决的问题。我们发现，对于具有过量卤化物空位的卤化物钙钛矿薄膜，光照后费米能级可移动高达0.7电子伏特。光照关闭后，这些缺陷能够捕获光载流子长达数小时。钙钛矿薄膜表面的卤化物空位对光载流子的捕获解释了巨大的光致费米能级移动和长时间的电子捕获现象。这种缺陷 - 光载流子复合体的形成会导致晶格变形以及缺陷态的能量移动。整个过程类似于在缺陷位点形成极化子。我们的数据还表明，这些被俘获的载流子可能通过提高缺陷迁移率来增加晶格的电极化率。
