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The development of perovskite light‐emitting diodes (PeLEDs) with both high efficiency and excellent stability remains challenging. Herein, a strong correlation between the lattice strain in perovskite films and the stability of resulting PeLEDs is revealed. Based on high‐efficiency PeLEDs, the device lifetime is optimized by rationally tailoring the lattice strain in perovskite films. A PeLED with a high peak external quantum efficiency of 18.2% and a long lifetime of 151 h (T70, under a current density of 20 mA cm−2) is realized with a minimized lattice strain in the perovskite film. In addition, an increase in the lattice strain is found during the long‐time device stability test, indicating that the degradation of the local perovskite lattice structure could be one of the degradation mechanisms for long‐term stable PeLEDs. [ABSTRACT FROM AUTHOR]

Effective modification of the structure and properties of halide perovskites via the pressure engineering strategy has attracted enormous interest in the past decade. However, sufficient effort and insights regarding the potential properties and applications of the high‐pressure amorphous phase are still lacking. Here, the superior and tunable photoelectric properties that occur in the pressure‐induced amorphization process of the halide perovskite Cs3Bi2I9 are demonstrated. With increasing pressure, the photocurrent with xenon lamp illumination exhibits a rapid increase and achieves an almost five orders of magnitude increment compared to its initial value. Impressively, a broadband photoresponse from 520 to 1650 nm with an optimal responsivity of 6.81 mA W−1 and fast response times of 95/96 ms at 1650 nm is achieved upon successive compression. The high‐gain, fast, broadband, and dramatically enhanced photoresponse properties of Cs3Bi2I9 are the result of comprehensive photoconductive and photothermoelectric mechanisms, which are associated with enhanced orbital coupling caused by an increase in BiI interactions in the [BiI6]3− cluster, even in the amorphous state. These findings provide new insights for further exploring the potential properties and applications of amorphous perovskites. [ABSTRACT FROM AUTHOR]

Herein, it is shown how a proton transfer process between the organic moiety in 3D methylammonium lead halide perovskite and the introduced aliphatic alkylamines provides the basis for a fabrication route toward hybrid 3D/2D perovskites and finally purely 2D Ruddlesden–Popper (RP) perovskite phases, predominantly the n = 1 phase. Five alkylamines with varying aliphatic chain lengths, such as butylamine, octylamine, dodecylamine, hexadecylamine, and octadecylamine as antisolvents in toluene, are used, which quickly protonate during the spin‐coating deposition of thin perovskite films. Formation of hydrogen bonds between protonated alkylamines and lead halide slabs leads to mixed 3D/2D hybrid perovskites, where the ratio between the 3D and 2D phases can be adjusted by the concentration of the alkylamine containing antisolvents. Longer‐chain aliphatic alkylamines (12 carbon atoms or greater) are most prone to slice 3D perovskite into layered perovskites with efficient green emission reaching up to 38% for their photoluminescence quantum yield in films. Above a certain concentration threshold, 3D perovskite can be completely modified into 2D RP perovskite phases with crystalline orientation parallel to the substrate. The introduced facile perovskite phase modification approach provides a convenient way toward different kinds of 2D RP metal halide perovskite films with attractive optical properties. [ABSTRACT FROM AUTHOR]

One‐dimensional semiconductor nanostructures have already been used for a variety of optoelectronic applications. Metal halide perovskites have emerged in recent years as promising high‐performance optoelectronic materials, but reports on 1D nanorods (NRs) of all‐inorganic halide perovskites are still scarce. This work demonstrates a synthetic strategy toward cesium‐based inorganic perovskite NRs by exploiting composition‐controlled crystal phase engineering. It is accomplished for Cd‐rich mixed‐cation CsPb1‐xCdxBr3 nanocrystals, where the initial 1D hexagonal perovskite phase drives the growth of the 1D NRs, as supported by first‐principles calculations. The band gaps of the resulting NRs are tunable by varying the Cd‐content, and the highly uniform CsPb0.08Cd0.92Br3 NRs (with an average length of 84 nm and width of 16 nm) exhibit a true blue‐color emission centered at 460 nm, with a high quantum yield of 48%. Moreover, this work also demonstrates the tunability of the Fermi levels in the films made of CsPb1‐xCdxBr3 alloyed nanocrystals, where samples with highest Cd content show an increase of the electron concentration and a related increase in the conductivity. [ABSTRACT FROM AUTHOR]

Organic ammonium cations play a vital role in building structures and tuning energy bands of organic–inorganic halide perovskites and the consequent photoelectric characteristics. Here, two 2D lead bromide perovskites: flat‐layered (BDA)PbBr4 (BDA = 1, 4‐butanediammonium), corrugation‐layered (PDA)7Pb6Br26 (PDA = 1, 3‐propanediammonium) and a 1D nanobelt‐shaped (EDA)2PbBr6 (EDA = ethylenediammonium) are built to explore their tunable structure, energy bands, and photoluminescence by a series of linear alkyl diammonium cations. Significant "spatial effect" of diammonium cations directly controls the space configurations of these lead bromide perovskites. From 2D (100)‐flat to 1D (110)‐nanobelt, distortions and disconnections of lead bromide layers are beneficial to the quantum confinement and generation of self‐trapping exciton (STE) energy levels of low‐dimensional perovskites. Upon ultraviolet excitation, (BDA)PbBr4, (PDA)7Pb6Br26, and (EDA)2PbBr6 exhibit blue, broadband yellowish white, and "warm" white emissions, respectively. Density functional theory combining STE theory demonstrates their bandgap changes and emission mechanisms. This work provides a basis for tuning the structure of low‐dimensional organic–inorganic halide perovskites for better photochromic properties. [ABSTRACT FROM AUTHOR]

To eliminate the toxic Pb2+ cation in hybrid halide perovskites, M′3+ cations of Bi/Sb‐based layered halide perovskites are being increasingly investigated for optoelectronic applications. However, such M′3+ trivalent cations constrain the face‐sharing bioctahedral or the bi‐layered perovskites required to meet the charge neutrality condition. This usually gives rise to oversized indirect bandgaps and inferior carrier transport. Recent experiment suggested a mixed‐cation tri‐layered halide perovskite can be obtained by sandwiching a [Cu2+X6]4− layer between Sb3+ perovskite bilayers along the polar [111] planes with cation ordering. A material design of mixed‐cation <111>‐oriented tri‐layered Pb‐free halide perovskite A4MM′2X12 is studied by a computational screening of various combinations of M2+ cations (e.g., Zn2+, Sn2+) and M′3+ cations (e.g., Bi3+, Sb3+). The thermodynamic stability of the candidate materials is systemically evaluated with respect to potential decomposition pathways and a series of stable compounds is synthesized. These results further indicate the chemical trend of electronic structure and how octahedral tilting coupling with charge ordering affects electronic properties. A protocol for engineering A4MM′2X12 perovskites with optimized structures and electronic properties by exploiting octahedral tilting coupling with charge ordering in the polar <111> layered perovskites is established. [ABSTRACT FROM AUTHOR]

Recently, the halide perovskites have increasingly received attention because of their superior capabilities in photodetector applications. However, the well‐known instability and lead‐toxicity are two major obstacles for their commercialization and practical applications. In this work, self‐powered photodetectors based on solution‐processed double perovskite Cs2AgBiBr6 films are fabricated for the first time. Owing to the high material integrity of Cs2AgBiBr6 and efficient interfacial charge transfer from perovskite to the underlying electron‐quenching layer, the photodetector demonstrates excellent performances. Especially, the unencapsulated device demonstrates a good working stability in the open air. Typically it has the ability to endure a high temperature of 373 K for 10 h continuous running, demonstrating a good temperature resistance. In addition, after 3‐month storage in open air, the photodetection capability of the device can almost be maintained. By deploying the photodetector as a point‐like sensing pixel, high‐resolution imaging patterns are acquired, which is the first report on imaging applications of lead‐free perovskite photodetectors. The obtained results suggest that the lead‐free double perovskite Cs2AgBiBr6 is potentially an attractive candidate to be applied in high‐efficiency and stable photodetectors that can be employed in optical imaging. [ABSTRACT FROM AUTHOR]

Lead‐free halide double perovskites with diverse electronic structures and optical responses, as well as superior material stability show great promise for a range of optoelectronic applications. However, their large bandgaps limit their applications in the visible light range such as solar cells. In this work, an efficient temperature‐derived bandgap modulation, that is, an exotic fully reversible thermochromism in both single crystals and thin films of Cs2AgBiBr6 double perovskites is demonstrated. Along with the thermochromism, temperature‐dependent changes in the bond lengths of AgBr (RAgBr) and BiBr (RBiBr) are observed. The first‐principle molecular dynamics simulations reveal substantial anharmonic fluctuations of the RAgBr and RBiBr at high temperatures. The synergy of anharmonic fluctuations and associated electron–phonon coupling, and the peculiar spin–orbit coupling effect, is responsible for the thermochromism. In addition, the intrinsic bandgap of Cs2AgBiBr6 shows negligible changes after repeated heating/cooling cycles under ambient conditions, indicating excellent thermal and environmental stability. This work demonstrates a stable thermochromic lead‐free double perovskite that has great potential in the applications of smart windows and temperature sensors. Moreover, the findings on the structure modulation‐induced bandgap narrowing of Cs2AgBiBr6 provide new insights for the further development of optoelectronic devices based on the lead‐free halide double perovskites. Thermochromic lead‐free double perovskites that have potential applications in smart windows and temperature sensors are demonstrated. The anharmonic fluctuations and associated strong electron–phonon coupling, combined with the spin–orbit coupling effect, are responsible for the thermochromism. The findings on the structure modulation‐induced bandgap narrowing of Cs2AgBiBr6 provide new insights for the development of optoelectronic devices based on double perovskites. [ABSTRACT FROM AUTHOR]

Effective modification of the structure and properties of halide perovskites via the pressure engineering strategy has attracted enormous interest in the past decade. However, sufficient effort and insights regarding the potential properties and applications of the high‐pressure amorphous phase are still lacking. Here, the superior and tunable photoelectric properties that occur in the pressure‐induced amorphization process of the halide perovskite Cs3Bi2I9 are demonstrated. With increasing pressure, the photocurrent with xenon lamp illumination exhibits a rapid increase and achieves an almost five orders of magnitude increment compared to its initial value. Impressively, a broadband photoresponse from 520 to 1650 nm with an optimal responsivity of 6.81 mA W−1 and fast response times of 95/96 ms at 1650 nm is achieved upon successive compression. The high‐gain, fast, broadband, and dramatically enhanced photoresponse properties of Cs3Bi2I9 are the result of comprehensive photoconductive and photothermoelectric mechanisms, which are associated with enhanced orbital coupling caused by an increase in BiI interactions in the [BiI6]3− cluster, even in the amorphous state. These findings provide new insights for further exploring the potential properties and applications of amorphous perovskites. [ABSTRACT FROM AUTHOR]