Millimeter-sized PbI2 flakes and Pb5S2I6 nanowires for flexible photodetectors

Abstract

Large-area and high-quality 2D layered materials with good electrical performance are necessary although active 2D materials for devices are usually limited to micrometer-sizes. Herein, large-size layered-crystalline lead(II) iodide (PbI₂) flakes with sizes of up to 5 mm were synthesized via a hydrothermal method. Thiourea facilitated their large-area growth. Photocurrent measurements of a PbI₂ flake photodetector (PD) constructed on flexible polyimide (PI) substrates exhibit a responsivity at 510 nm of up to 5 mA W⁻¹. Additionally, the fast response speed of the device is less than 30 ms. Low dark currents are lower than 10 pA at a bias of 5 V. The spectral selectivity of our PbI₂ flakes may potentially be used for narrowband photodetection. The process can also be converted to produce Pb₅S₂I₆ nanowires (NWs) with a broadened spectral response range by changing the ratio of reactants. Our results on the freestanding growth of large area PbI₂ flakes and Pb₅S₂I₆ NWs may lead to facile flexible device fabrication possibilities. These findings will broaden our fundamental knowledge of van der Waals layered halide semiconductors. Meanwhile, such a hydrothermal synthetic approach paves a practical route towards large-area promising organic–inorganic perovskite, which is hosted by PbI₂.