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

Due to the possibility to be thin down to the atomic thickness, exhibiting fascinating chemical and physical properties, layered materials have attracted extensive amounts of attentions. In particular, PbI2, a kind of layered material, and its perovskite derivatives, CH3NH3PbI3 (i.e. MAPbI3), have been demonstrated with excellent photoresponsivities for efficient photodetection as well as photovoltaic devices. In this work, we report the successful synthesis of large-scale, highly-dense and freestanding PbI2 nanosheets by manipulating the local surface reaction kinetics during the growth by physical vapor deposition. As contrasted to the conventional 2D growth along the substrate surface, we synthesize the nanosheets via effective nucleation of micro-planes with different angles relative to the in-plane direction of underlying rough-surfaced substrates. This results in freestanding nanosheets with high-density. Meanwhile, the synthesized PbI2 nanosheets are highly crystalline with superior photosensing characteristics. When configured into photodetectors, the fabricated photodetector exhibits a photoresponsivity of 410 mA/W, a detectivity of 3.1×1011 Jones, and a fast response with the rise and decay time constants of 86 ms and 150 ms, respectively, under a wavelength of 405 nm. In addition, these PbI2 nanosheets can also be completely converted into MAPbI3 materials via chemical vapor deposition with a strong photoluminescence and an improved photoresponsivity up to 40 A/W. The impressive performance parameters of the PbI2 nanosheet are competitive to those of state-of-the-art layered materials based photodetectors, revealing the technological potency of these freestanding nanosheets for next-generation high-performance optoelectronics.