Flexible photodetectors based on phase dependent PbI2 single crystals

As a precursor of perovskites, lead iodide (PbI2) is a typical layered material with a direct bandgap. Perovskites are widely utilized in highly efficient photovoltaics, but the low-dimensional PbI2 nanostructures and their (opto)electronic properties are rarely reported. Herein, single-crystalline PbI2 nanosheets (phase I) and nanowires (phase II) are controllably synthesized via a facile physical vapor deposition method. Their different crystal morphology and crystallographic symmetry show obvious phase dependence. The corresponding photodetectors on both SiO2/Si and flexible polyethylene terephthalate (PET) substrates are investigated systematically. Compared with PbI2 nanowire based photodetectors, PbI2 nanosheet based photodetectors exhibit a relatively high sensitivity (with a high photoresponsivity of 147.6 A W−1 and fast response time) to the 450 nm laser. Both the PbI2 nanosheet and nanowire devices with flexible PET substrates exhibit comparable performance to their photodetectors fabricated on SiO2/Si, and also show excellent mechanical stability and durability. At the same time, the photoelectric properties vary greatly with different bending angles for such flexible PbI2 photodetectors. By modeling the band structures under different compressive strains, the theoretical simulations fit very well with experimental results. These findings provide a scientific basis for exploiting high-performance flexible photodetectors based on low-dimensional PbI2 single crystals.