刘生忠EcoMat：二维卤化铅钙钛矿单晶研究进展：晶体生长、物理性能及器件应用
The following article is from EcoMat Author EcoMat
成果简介
近年来，有机-无机卤化铅二维（2D）钙钛矿的研究如火如荼。二维钙钛矿具有与三维钙钛矿完全不同的层状结构，有机层和无机层交错，使得二维钙钛矿材料更稳定并具有各向异性的电传输。同时，二维有机-无机卤化铅钙钛矿单晶因其电荷载流子寿命长、缺陷密度低和光致发光量子产率高等显着特性而受到越来越多的关注，提高了它们在光电应用中的潜力。此前，一系列基于二维钙钛矿单晶的材料体系已被合成并应用于各种器件中。鉴于此，西安电子科技大学常晶晶教授与陕西师范大学刘生忠教授合作在EcoMat发表了题为“Recent progress of two-dimensional lead halide perovskite single crystals: Crystal growth, physical properties, and device applications”的综述文章，讨论了有机-无机卤化铅二维钙钛矿单晶的制备方法、生长原理、光电性能和几种器件应用。
内容详情
FIGURE 1 (PEA)2(MA)n−1PbnI3n+1 perovskite as an example. A, Schematic diagram of the unit cell structures for different n values, which shows the evolution of dimensionality from 2D (n = 1) to 3D (n = ∞). B, DFT simulation of the formation energy of perovskites with different n values in different atmospheres.
FIGURE 2 A, Optical images of (PEA)2PbI4･(MAPbI3)n−1(n=1,2,3) single crystals from top to bottom. B, Optical images of the (3AMP)(MA)n−1PbnI3n+1 and (4AMP)(MA)n−1PbnI3n+1 plate-like crystals (n=1,2,3)
FIGURE 3 A, Solubility of (PEA)2PbI4 SCM in GBL as a function of temperature. B, Solubility derivative with respect to temperature for (PEA)2PbI4 SCM in GBL. C, Photo of the (PEA)2PbI4 SCM sample (73×35 mm2). D, Schematic illustration of the IPC procedure to grow 2D layered (PEA)2PbI4 SCM. E, Photos of a (PEA)2PbI4 SCM taken at different stages of the growth process. F, Photo of a piece of (PEA)2PbI4 SCM, 3.5 μm in thickness, wrapped around a small tube (1.6 cm in diameter) to show its flexibility. G, A photo showing the flexing angle measurement for the (PEA)2PbI4 SCM. H, Schematic of the experimental procedure: 20 μL of (BA)2(MA)n−1PbnI3n+1 hydriodic acid solution drop on a 2×2 μm glass substrate covered with another. The device was placed in a drying oven at 80°C until all H2O and HI volatilized. I-K, Bright field microscopy images and fluorescence pictures (inset) of (BA)2(MA)n−1PbnI3n+1 (n = 1, 2, 3) single-crystal films, respectively. L, Schematic illustration of the scalable growth of single-crystal perovskite thin film arrays. Scale bar, 1 mm
FIGURE 4 A, Schematic diagram of the growth process of 2D (PEA)2PbBr4 perovskite single crystals by the AVC method; B, Photograph of a transparent, 2-mm (PEA)2PbBr4 single crystal made by the AVC method; C, SEM image of a (PEA)2PbBr4 single crystal prepared by AVC showing a layered structure; D, AFM image with the height profile of an exfoliated layer with a monolayer step of 1 nm, as shown in the inset; E, Photoluminescence of an exfoliated (PEA)2PbBr4 single-crystal layer. The PL peak of the exfoliated layer (∼40 nm) is slightly blue-shifted due to less self-absorption. F, Schematic diagram of the AVC process. G, Optical images of typical PEPI crystals obtained by the AVC method. H, Schematic diagram of the AVCC process. I, optical images of PEPI crystals obtained by the AVCC method. The size of the quartz plate is 25 mm × 25 mm. J, Schematic diagram of the growth process of the controlled-evaporation method of (PEA)2PbBr4 single crystals; K, Photograph of a transparent, ~27×11 mm2 (PEA)2PbBr4 single crystal made by the controlled-evaporation method; L, SEM image of the (PEA)2PbBr4 crystalline surface; M, SEM image of the (PEA)2PbBr4 single crystal showing a layered structure. Inset: Cross section SEM image of the (PEA)2PbBr4 single crystal
FIGURE 5 Crystallization of (PEA)2PbI4 perovskite single crystals. A, The Gibbs free energy change ΔGtotal as a function of particle radius. B, Graph illustrating the lower nucleation barrier for the solution surface compared with that in the solution volume. C, Schematic of the single crystal staying afloat on the solution surface. D, Schematic of the surface tension-controlled crystallization process. E, Photographs of the (PEA)2PbI4 perovskite single crystals grown at different temperatures. F, Corresponding photographs of (PEA)2PbI= perovskite single crystals completed at different temperatures
FIGURE 6 A, Schematic diagram of solubility and supersolubility; B, Mass and concentration of (PEA)2PbBr4 precursor solution as a function of evaporation time; C, Mass and growth rate of (PEA)2PbBr4 as a function of time; D, Schematic illustration of the alignment of butylammonium cation surfactant at the water-air interface for templating the nucleation. E, Experimental setup during nucleation. F, Molecular interaction between precursor molecules (red) and water molecules (yellow). Lower interaction energy is expected for the surface layer molecules due to the surface tension effect compared to those in bulk solution. G, Experimental setup during crystal growth. Graphic illustrations of H, the lower nucleation barrier, I, the larger free energy changes during crystal growth, and J, the higher growth rate of the precursor molecules at the water-air interface compared to those in bulk solution. K, Solubility of (PEA)2PbI4 in GBL as a function of temperature; L, Solubility derivative with respect to temperature for (PEA)2PbI4 in GBL
FIGURE 7 A, View of the unit cell. B, Band structure of BA2MA4Pb5I16 with and without SOC calculated. C, In-house X-ray diffraction pattern of selected individual crystals of BA2MA4Pb5I16 illustrates the tendency of the crystal toward twinning and growing domains normal to the plate-like crystals (scale bars=50 μm). D, J-V characteristics of the planar solar cells (under AM 1.5G illumination). E, Statistical graph for the solar cell figure of merit for 20 devices. F, External quantum efficiency (EQE) spectrum for a typical device and the integrated JSC calculated from the EQE on the basis of the solar spectrum
FIGURE 8 A, Schematic diagram of a vertical device with a graphene/2D perovskite/Au structure; B and C, Cross-sectional STEM images and corresponding EDX elemental profiles of the device, B, as produced and C, after pulsed voltage stress; D, AFM image showing a group of graphene/2D perovskite/Au resistive memory devices; E, Typical resistive switching curves for set and reset. F, Various program or set currents reported in the literature; G, Schematic illustration of the 2D (C4H9NH3)2PbBr4 photodetector with interdigital graphene electrodes; H, SEM image of the as-fabricated device, scale bar, 1 μm; I, The gap of two graphene electrodes is about 100 nm, scale bar, 1 μm; J, Current-voltage (ISD-VSD) curves of the individual device in the dark and under different illumination intensities from a 470-nm defocused laser; K, Time-dependent photocurrent response of the device with a 470-nm defocused laser of spot size 1 mm2, operated at a bias voltage of 0.5 V and a power of 10 μW; L, Enlarged view of the photocurrent response during on-off illumination switching
FIGURE 9 A and B, Schematic illustrations of the photoelectric process and photoconductivity gain in the Au/(PEA)2PbI4 SCM/Au device under light illumination; C, The current-voltage (I-V) curves of the device measured in the dark and under 460-nm wavelength illumination with various light intensities; D, EQE and D* for the photosensor with the incident light power density ranging from 8 × 10−5 to 310 mW cm−2 at a wavelength of 460 nm under a fixed 4 V bias; E, Absorbance spectrum of the (PEA)2PbI4 SCM and photoresponse spectrum of the photosensor illuminated using monochromatic light with wavelength ranging from 350 to 650 nm at 4 V bias; F, Temporal photocurrent response of the (PEA)2PbI4 SCM photosensor; G, Schematic diagram of the photodetector made using a (PEA)2PbBr4 single crystal; H, Voltage-current curves of the (PEA)2PbBr4 device illuminated using a 365-nm LED at different light intensities; I, Transient photocurrent of the photodetector at a bias of 10 V
FIGURE 10 A, Optical image of the exfoliated (BA)2(MA)n−1PbnI3n+1 with Ag contacts. B-D, Output characteristics of (BA)2(MA)n−1PbnI3n+1 single-crystal FETs under various Vbg values for B, n = 1, C, n = 2, and D, n = 3 at 77 K. E, Schematic illustration of the transport behavior of the (BA)2(MA)n−1PbnI3n+1 perovskite crystal for n = 1 to n = 3. Red arrows and their corresponding shading indicate the direction of current flow and intensity in the conduction channel, respectively
结论与展望
二维钙钛矿单晶材料因其卓越的性能和在光电应用中的巨大潜力而受到越来越多的关注。相较于三维钙钛矿，它们最显着的特点是天然量子阱和出色的防潮性。
二维钙钛矿单晶材料具有荧光寿命长、缺陷少、光致发光量子产率高等诸多优异性能。值得注意的是，3D钙钛矿单晶能够改变三个位点（不同的有机基团、金属、卤素）的元素并调整成分以获得具有不同性能的材料。相反，二维钙钛矿材料有两个有机分子的位点，大大增加了材料的多样性。通过改变大有机阳离子的类型，可以调整二维材料的带隙以获得所需的光电性能。因此，可以利用二维钙钛矿单晶元素的多样性来获得不同的材料性能，进一步扩展了二维钙钛矿单晶材料的应用范围。
对于二维钙钛矿单晶，未来的研究方向可以从以下几个方面考虑：
1. 对于一些二维材料，现有的制备方法需要找到一种特定的溶剂来溶解钙钛矿。例如在IPC法中，(PEA)2PbBr4溶解在GBL中，溶解度随温度升高而增加。要使用这种方法，需要找到一种溶解度随温度变化的溶剂。因此，将寻求可用于制备各种钙钛矿单晶的通用溶剂。
2．生长方式有待进一步优化以促进其商业化应用。本文讨论了很多二维钙钛矿单晶的生长方法，但都需要很长时间才能生长出大面积的单晶，因此需要进一步优化和缩短生长时间，以利于未来的大规模生产。
3. 可以利用二维钙钛矿材料的特性来寻求更多的器件应用。大面积柔性2D钙钛矿单晶的制备方法为高性能、柔性、单晶电子和可穿戴设备（包括显示器、触摸传感器件、晶体管等）的应用铺平了道路。对于2D/3D混合PSC，需要探索一种直接生长准2D钙钛矿单晶以减少缺陷并提高功率转换效率的方法。关于场效应管，据报道它们都是在毫米级以下的二维/准二维钙钛矿单晶上制造的，因此有必要开发简单、大面积、厚度可控的单晶膜，以用于进一步的场效应管应用。
文献信息
Jiayu Di, Jingjing Chang, Shengzhong (Frank) Liu,* Recent progress of two-dimensional lead halide perovskite single crystals: Crystal growth, physical properties, and device applications, EcoMat. 2020;2:e12036
原文链接：https://doi.org/10.1002/eom2.12036
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