Mapping Trap Dynamics in a CsPbBr<sub>3</sub> Single-Crystal Microplate by Ultrafast Photoemission Electron Microscopy
Wei Liu, Haoran Yu, Yaolong Li, Aiqin Hu, Wang Ju, Guowei Lü, Xiaofang Li, Hong Yang, Lun Dai, Shufeng Wang, Qihuang Gong
Abstract
For versatile lead-halide perovskite materials, their trap states, both in the bulk and at the surface, significantly influence optoelectronic behaviors and the performance of the materials and devices. Direct observation of the trap dynamics at the nanoscale is necessary to understand and improve the device design. In this report, we combined the femtosecond pump–probe technique and photoemission electron microscopy (PEEM) to investigate the trap states of an inorganic perovskite CsPbBr3 single-crystal microplate with spatial–temporal–energetic resolving capabilities. Several shallow trap sites were identified within the microplate, while the deep traps were resolved throughout the surface. The results revealed high-defect tolerance to the shallow traps, while the surface dynamics were dominated by the surface deep traps. The ultrafast PEEM disclosed a full landscape of fast electron transfer and accumulation of the surface trap states. These discoveries proved the excellent electronic properties of perovskite materials and the importance of surface optimization.