Flexible photodetectors based on phase dependent PbI2 single crystals

Abstract

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.