Waveguide Photodetector\nBased on Perovskite Single-Crystal\nHeterojunction

Perovskite\nsingle-crystal sheet (SCS) lateral-structured photodetector\ntypically needs to guide the signal light in free space to the SCS\nsurface for photoelectric conversion to realize photodetection. However,\nthe device performance in this working mode is highly dependent on\nthe surface state of the active layer. To overcome this potential\nissue, this study puts forward a strategy of MAPbBr<sub>3</sub>-MAPbI<sub>3</sub> SCS heterojunction waveguide (HWG), in which MAPbBr<sub>3</sub> SCS is utilized as the waveguide (WG) structure to couple the far-field\nsignal light into the confined near-field and propagates it to the\nactive layer as a planar WG, directly exciting the internal single-crystal\nlattices of MAPbI<sub>3</sub> SCS, without taking into account the\nsurface state. The device performance loss rate is 6 dB/mm, and its\noptimal performance can be increased by 60 times compared to that\nwhen light is guided to surface mode. Additionally, based on the visible\nlight transparency and water insolubility of PbBr<sub>2</sub>, this\nstudy also verified the feasibility of PbBr<sub>2</sub>-MAPbI<sub>3</sub> HWG devices. Despite the suboptimal structural geometry of\nthe PbBr<sub>2</sub> wire cluster leading to an increased loss rate\nof 11.3 dB/mm, the device encapsulated with silicone sealant demonstrates\nconsiderable stability, with the performance decaying by only 7% after\nbeing immersed in the water for 100 h. The findings of this study\nsuggest that the constructed SCS-HWG configuration provides a feasible\narchitecture for high-performance SCS photodetectors.