Flexible photodetectors based on phase dependent Pbl(2) single crystals

As a precursor of perovskites, lead iodide (Pbl(2)) is a typical layered material with a direct bandgap. Perovskites are widely utilized in highly efficient photovoltaics, but the low-dimensional Pbl(2) nanostructures and their (opto)electronic properties are rarely reported. Herein, single-crystalline Pbl(2) 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 Pbl(2) nanowire based photodetectors, Pbl(2) 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 Pbl(2) 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 Pbl(2) 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 Pbl(2) single crystals.