Large-Scale Synthesis of Freestanding Layer-Structured PbI2 and MAPbI3 Nanosheets for High-Performance Photodetection.

Recently, due to the possibility of thinning down to the atomic thickness to achieve exotic properties, layered materials have attracted extensive research attention. In particular, PbI2 , a kind of layered material, and its perovskite derivatives, CH3 NH3 PbI3 (i.e., MAPbI3 ), have demonstrated impressive photoresponsivities for efficient photodetection. Herein, the synthesis of large-scale, high-density, and freestanding PbI2 nanosheets is demonstrated by manipulating the microenvironment during physical vapor deposition. In contrast to conventional two-dimensional (2D) growth along the substrate surface, the essence here is the effective nucleation of microplanes with different angles relative to the in-plane direction of underlying rough-surfaced substrates. When configured into photodetectors, the fabricated device exhibits a photoresponsivity of 410 mA W-1 , a detectivity of 3.1 × 1011 Jones, and a fast response with the rise and decay time constants of 86 and 150 ms, respectively, under a wavelength of 405 nm. These PbI2 nanosheets can also be completely converted into MAPbI3 materials via chemical vapor deposition with an improved photoresponsivity up to 40 A W-1 . All these performance parameters are comparable to those of state-of-the-art layered-material-based photodetectors, revealing the technological potency of these freestanding nanosheets for next-generation high-performance optoelectronics.