Kai Wang

The robust material stability of the quasi-two-dimensional (quasi-2D) metal halide perovskites has opened the possibility for their usage instead of three-dimensional (3D) perovskites. Further, devices based on large area single crystal membranes have shown increasing promise for photoelectronic applications. However, growing inch-scale quasi-2D perovskite single crystal membranes (quasi-2D PSCMs) has been fundamentally challenging. Here we report a fast synthetic method for synthesizing inch-scale quasi-2D PSCMs, namely (C4H9NH3)n(CH3NH3)n−1PbnI3n+1 (index n = 1, 2, 3, 4, and ∞), and demonstrate their application in a single-crystal photodetector. Additionally, we found that the sharp edges of the 2D single crystals exhibit extraordinarily large free charge carrier density of ~10^20 cm-3. This characteristic is significantly different from the bulk region in classical multiple quantum well (MQW) system where electron-holes pairs are tightly bonded through the Coulomb interaction forming the excitons. The 2D MQW layer edge is not related to the surface charge accumulation rather it is associated to the local nontrivial energetic states in the electronic structure of the layer edges.