High‐Performance Flexible Photodetectors based on High‐Quality Perovskite Thin Films by a Vapor–Solution Method

Organometal halide perovskites are new light‐harvesting materials for lightweight and flexible optoelectronic devices due to their excellent optoelectronic properties and low‐temperature process capability. However, the preparation of high‐quality perovskite films on flexible substrates has still been a great challenge to date. Here, a novel vapor–solution method is developed to achieve uniform and pinhole‐free organometal halide perovskite films on flexible indium tin oxide/poly(ethylene terephthalate) substrates. Based on the as‐prepared high‐quality perovskite thin films, high‐performance flexible photodetectors (PDs) are constructed, which display a nR value of 81 A W^?1 at a low working voltage of 1 V, three orders higher than that of previously reported flexible perovskite thin‐film PDs. In addition, these flexible PDs exhibit excellent flexural stability and durability under various bending situations with their optoelectronic performance well retained. This breakthrough on the growth of high‐quality perovskite thin films opens up a new avenue to develop high‐performance flexible optoelectronic devices.     

High‐Performance Inorganic Perovskite Quantum Dot–Organic Semiconductor Hybrid Phototransistors

All‐inorganic lead halide perovskite quantum dots (IHP QDs) have great potentials in photodetectors. However, the photoresponsivity is limited by the low charge transport efficiency of the IHP QD layers. High‐performance phototransistors based on IHP QDs hybridized with organic semiconductors (OSCs) are developed. The smooth surface of IHP QD layers ensures ordered packing of the OSC molecules above them. The OSCs significantly improve the transportation of the photoexcited charges, and the gate effect of the transistor structure significantly enhances the photoresponsivity while simultaneously maintaining high I _photo/I _dark ratio. The devices exhibit outstanding optoelectronic properties in terms of photoresponsivity (1.7 × 10⁴ A W^?1), detectivity (2.0 × 10¹⁴ Jones), external quantum efficiency (67000%), I _photo/I _dark ratio (8.1 × 10⁴), and stability (100 d in air). The overall performances of our devices are superior to state‐of‐the‐art IHP photodetectors. The strategy utilized here is general and can be easily applied to many other perovskite photodetectors.     

Spatially Confined Growth of Fullerene to Super‐Long Crystalline Fibers in Supramolecular Gels for High‐Performance Photodetector

As a superstar organic semiconductor, fullerene (C₆₀) is versatile in nature for its multiple photoelectric applications. However, owing to its natural 0D structure, a challenge still remains unbeaten as to growth of 1D fullerene crystals with tunable sizes. Herein, reported is an efficient approach to grow C₆₀ as super‐long crystalline fibers with tunable lengths and diameters in supramolecular gel by synergic changes of anti‐solvent, gel length, crystallization time or fullerene concentration. As a result, the crystalline C₆₀ fibers can be modulated to as long as 70 mm and 70 000 in their length‐to‐width ratio. In this case, the gel 3D network provides spatial confinements for the growth of 1D crystal along the directional dispersion of anti‐solvent. The fabricated fullerene device exhibits high responsivity (2595.6 mA W^‐1) and high specific detectivity (2.7 × 10¹² Jones) at 10 V bias upon irradiation of 400 nm incident light. The on/off ratio and its quantum efficiency are near to 540 and about 800%, respectively, and importantly, its photoelectric property remains very stable after storage in air for six months. Therefore, spatially confined growth of fullerene in supramolecular gels will be another crucial strategy to synthesize 1D semiconductor crystals for photoelectrical device applications in near future.     

Gradient Energy Band Driven High‐Performance Self‐Powered Perovskite/CdS Photodetector

Self‐powered photodetectors are highly desired to meet the great demand in applications of sensing, communication, and imaging. Manipulating the carrier separation and recombination is critical to achieve high performance. In this paper, a self‐powered photodetector based on the integrated gradient O‐doped CdS nanorod array and perovskite is presented. Through optimizing the degree of continuous built‐in band bending in the gradient‐O CdS, the photodetector demonstrates a remarkable detectivity of 2.1 × 10¹³ Jones. Under the self‐powered voltage mode, the responsivity can be as high as 0.48 A W^?1, and the rise and decay time are 0.54/2.21 ms. The comprehensive performance is comparable and even better than reported perovskite and other types of self‐powered photodetectors. The improved mechanism reveals that the gradient band bending promotes the photogenerated carrier transfer and hinders the recombination at the interface.     

Controlling Nucleation and Growth of Metal Halide Perovskite Thin Films for High‐Efficiency Perovskite Solar Cells

Metal halide perovskite thin films can be crystallized via a broad range of solution‐based routes. However, the quality of the final films is strongly dependent upon small changes in solution composition and processing parameters. Here, this study demonstrates that a fractional substitution of PbCl₂ with PbI₂ in the 3CH₃NH₃I:PbCl₂ mixed‐halide starting solution has a profound influence upon the ensuing thin‐film crystallization. The presence of PbI₂ in the precursor induces a uniform distribution of regular quadrilateral‐shaped CH₃NH₃PbI₃ perovskite crystals in as‐cast films, which subsequently grow to form pinhole‐free perovskite films with highly crystalline domains. With this new formulation of 3CH₃NH₃I:0.98PbCl₂:0.02PbI₂, this study achieves a 19.1% current–voltage measured power conversion efficiency and a 17.2% stabilized power output in regular planar heterojunction solar cells.     

2D Porous TiO2 Single‐Crystalline Nanostructure Demonstrating High Photo‐Electrochemical Water Splitting Performance

Porous single crystals are promising candidates for solar fuel production owing to their long range charge diffusion length, structural coherence, and sufficient reactive sites. Here, a simple template‐free method of growing a selectively branched, 2D anatase TiO₂ porous single crystalline nanostructure (PSN) on fluorine‐doped tin oxide substrate is demonstrated. An innovative ion exchange–induced pore‐forming process is designed to successfully create high porosity in the single‐crystalline nanostructure with retention of excellent charge mobility and no detriment to crystal structure. PSN TiO₂ film delivers a photocurrent of 1.02 mA cm^?2 at a very low potential of 0.4 V versus reversible hydrogen electrode (RHE) for photo‐electrochemical water splitting, closing to the theoretical value of TiO₂ (1.12 mA cm^?2). Moreover, the current–potential curve featuring a small potential window from 0.1 to 0.4 V versus RHE under one‐sun illumination has a near‐ideal shape predicted by the Gartner Model, revealing that the charge separation and surface reaction on the PSN TiO₂ photoanode are very efficient. The photo‐electrochemical water splitting performance of the films indicates that the ion exchange–assisted synthesis strategy is effective in creating large surface area and single‐crystalline porous photoelectrodes for efficient solar energy conversion.     

Morphology Engineering for High‐Performance and Multicolored Perovskite Light‐Emitting Diodes with Simple Device Structures

The film morphology is extremely significant for solution processed perovskite devices. Through fine morphology engineering without using any additives or further posttreatments, a full‐coverage and high quantum yield perovskite film has been achieved based on one‐step spin‐coating method. The morphologies and film characteristics of MAPbBr₃ with different MABr:PbBr₂ starting material ratios are in‐depth investigated by scanning electron microscopy, atomic force microscopy, X‐ray diffraction, photoluminescence, and time resolved photoluminescence. High performance organometal halide perovskite light‐emitting didoes (PeLEDs) based on simple device structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/perovskite/TPBi/Ca/Al are demonstrated. The green PeLED based on MAPbBr₃ shows a maximum luminance of 8794 cd m^?2 (at 7.3 V) and maximum current efficiency of 5.1 cd A^?1 (at 5.1 V). Furthermore, a class of hybrid PeLEDs by adjusting the halide ratios of methylammonium lead halide (MAPbX₃, where X is Cl, Br, or I) are also demonstrated at room temperature. These mix‐halogenated PeLEDs show bright luminance (above 100 cd m^?2) with narrow and clean emission bands over the wide color gamut.     

High‐Performance Solution‐Processed Organo‐Metal Halide Perovskite Unipolar Resistive Memory Devices in a Cross‐Bar Array Structure

Resistive random access memories can potentially open a niche area in memory technology applications by combining the advantages of the long endurance of dynamic random‐access memory and the long retention time of flash memories. Recently, resistive memory devices based on organo‐metal halide perovskite materials have demonstrated outstanding memory properties, such as a low‐voltage operation and a high ON/OFF ratio; such properties are essential requirements for low power consumption in developing practical memory devices. In this study, a nonhalide lead source is employed to deposit perovskite films via a simple single‐step spin‐coating method for fabricating unipolar resistive memory devices in a cross‐bar array architecture. These unipolar perovskite memory devices achieve a high ON/OFF ratio up to 10⁸ with a relatively low operation voltage, a large endurance, and long retention times. The high‐yield device fabrication based on the solution‐process demonstrated here will be a step toward achieving low‐cost and high‐density practical perovskite memory devices.