Multifunctional and High-Performance FAPBI₃ Quantum Dots/Graphene UV Photodetectors by the Modulation of Photoconductivity

Low-dimensional devices with different photoconductive effects attract much attention in optoelectronics. In this work, negative photoconductivity (NPC) monolayer graphene photodetectors are fabricated by chemical vapor deposition (CVD), and a positive photoconductivity (PPC) photodetector is realized by decorating perovskite FAPbI₃ quantum dots prepared by a simple and cost-effective non-polar solvent synthesis method on a graphene surface. The graphene-based photodetector exhibits an NPC characteristic, which is attributed to the absorption and desorption of water molecules on the graphene surface. The responsivity of the photodetector with an NPC characteristic is −0.86 A W⁻¹ under intense ultraviolet light irradiation, and the detectivity is −2.45 × 10⁹ Jones. The FAPbI₃ quantum dots/graphene photodetector with a PPC feature has a responsivity of 8.03 A W⁻¹ and a detectivity of 1.89 × 10¹⁰ Jones under the irradiation of ultraviolet light of 365 nm and 55.3 mW cm⁻² intensity. Due to the intense light absorption of perovskite combined with the extremely high mobility of graphene, photodetectors have high exciton separation and photocurrents when the devices are irradiated by ultraviolet light. Individual photodetectors are successfully created with NPC and PPC effects; the critical analysis for the different photoconductive mechanisms is provided, which will benefit the development of future multifunctional systems.