Two-step vapor deposition of self-catalyzed large-size PbI2 nanobelts for high-performance photodetectors

Abstract

The grown lead iodide (PbI₂) is usually a two-dimensional sheet with a finite size which necessitates sophisticated device metallization and the growth of quasi one-dimensional materials is still challenging. In this work, large-size (length > 100 μm), single-crystalline and high-density PbI₂ nanobelts are successfully synthesized by manipulating the microenvironment in a two-step vapor deposition process at a slow heating rate of ∼18 °C min⁻¹. Firstly, PbI₂ nanosheet seeds are grown by physical vapor deposition, and then PbI₂ nanobelts are synthesized by a self-catalyzed vapor–liquid–solid growth mechanism, which is verified by the Pb nanoparticles on the nanobelt tips. Photoluminescence and ultraviolet-visible spectra show the uniform high-quality crystallinity of the as-prepared large-size PbI₂ nanobelts with a bandgap of 2.36 eV. When configured into photodetectors with a shadow mask, the fabricated device exhibits a low dark current of 4 pA, an impressive ON/OFF current ratio of 10³–10⁴, a photoresponsivity of 13 mA W⁻¹, and a fast response with the rise and decay time constants of 425 and 41 ms, respectively. All these performances are comparable to those of state-of-the-art layered PbI₂ nanostructure photodetectors, but the ease of synthesizing large-size PbI₂ nanobelts may have a useful impact on next-generation easily-fabricated high-performance optoelectronics.