Characterization of highly crystalline lead iodide nanosheets prepared by room-temperature solution processing

Abstract

Two-dimensional semiconducting materials are particularly appealing for many applications.Although theory predicts a large number of two-dimensional materials, experimentally only a few of these materials have been identified and characterized comprehensively in the ultrathin limit. Lead iodide, which belongs to the transition metal halides family and has a direct bandgap in the visible spectrum, has been known for a long time and has been well characterized in its bulk form. Nevertheless, studies of this material in the nanometer thickness regime are rather scarce. In this article we demonstrate an easy way to synthesize ultrathin, highly crystalline flakes of PbI2 by precipitation from a solution in water. We thoroughly characterize the produced thin flakes with different techniques ranging from optical and Raman spectrosThis is the post-peer reviewed version of the following article: R. Frisenda et al., "Characterization of highly crystalline lead iodide nanosheets prepared by room-temperature solution processing" Nanotechnology (2017) https://dx.doi.org/10.1088/1361-6528/aa8e5c 2 copy to temperature-dependent photoluminescence and electron microscopy. We compare the results to ab initio calculations of the band structure of the material. Finally, we fabricate photodetectors based on PbI2 and study their optoelectronic properties.

Low‐Temperature Heteroepitaxy of 2D PbI2/Graphene for Large‐Area Flexible Photodetectors

“…However, the major obstacles to obtaining a large‐area uniform PbI 2 film with good crystallinity, especially, on flexible transparent electrodes, remain to be overcome . On the other hand, as a promising flexible transparent electrode, the graphene film has a dangling bond‐free surface and contains in‐plane hexagonally packed structures, which may facilitate the vdWs epitaxy of PbI 2 and produce 2D forms due to the relatively lower energy barrier for lateral growth . Moreover, the impenetrability and high mobility of graphene have reportedly enhanced the stability and response speed of 2D PbI 2 /graphene heterostructures .…”

“…Monolayer graphene showed typical hexagonal rings comprising carbon atoms with a lattice spacing of ≈0.21 nm, while PbI 2 exhibited hexagonal rings comprising Pb and I atoms, with two in‐plane adjacent Pb (or I) atoms ≈0.23 nm apart. These results were in agreement with their reported lattice parameters . The fast Fourier transform (FFT) of the TEM images further confirmed the heteroepitaxy growth and high crystallinity of the PbI 2 deposited on the graphene film under the modulation of lattice‐match engineering.…”

Growth of Ultraflat PbI2 Nanoflakes by Solvent Evaporation Suppression for High‐Performance UV Photodetectors

“…Figure d exhibits time‐dependent photocurrent measurement on the PbI 2 ‐based photodetector under different power densities of a 375 nm laser with V ds = 5 V and V g = 0 V. We calculated the responsivity and detectivity of our PbI 2 photodetector using the formula and , in which R stands for responsivity, I light is the current under illumination, I dark is the dark current, P represents the power density of the 375 nm laser, S denotes the effective area of the PbI 2 channel (Figure b), and e is the element charge. Responsivity and detectivity are as high as 0.51 A W −1 and 4.0 × 10 10 Jones at V ds = 5 V and P = 6.37 mW cm −2 , which are superior to most of the reported photodetectors . Another critical parameter used to evaluate the light response property of a photodetector is EQE.…”

“…Different from the properties of TMDs like MoS 2 and WSe 2 which experience an indirect to direct bandgap change when the layer number is reduced to monolayer, multilayered PbI 2 is a direct bandgap semiconductor while the monolayer counterpart owns an indirect bandgap . Thus, multilayered PbI 2 is favorable for constructing UV photodetectors with a higher light absorbance capability than the monolayer counterpart …”

“…Compared with the conventional mechanical exfoliation and PVD methods, liquid‐phase growth method does not require high temperature, vacuum, or complicated apparatus, which is not only facile to handle but also compatible with almost all kinds of growth substrates. For example, Frisenda et al obtained PbI 2 nanoflakes with varied thicknesses by directly dropping 100 °C saturated PbI 2 solution onto a target substrate, although the surface of the PbI 2 nanoflakes obtained through this way was very rough. According to the classical band theory, the broken structure symmetry due to surface roughness and internal defects can produce inevitable defect states, resulting in easily trapped carriers and deteriorated optoelectronic properties.…”