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Decreasing perovskite nanocrystal size increases radiative recombination due to the quantum confinement effect, but also increases the Auger recombination rate which leads to carrier imbalance in the emitting layers of electroluminescent devices. Here, we overcome this trade‐off by increasing the exciton effective mass without affecting the size, which is realized through the trace Cd2+ doping of formamidinium lead bromide perovskite nanocrystals. We observe an ~2.7 times increase in the exciton binding energy benefiting from a slight distortion of the [BX6]4− octahedra caused by doping in the case of that the Auger recombination rate is almost unchanged. As a result, bright color‐saturated green emitting perovskite nanocrystals with a photoluminescence quantum yield of 96 % are obtained. Cd2+ doping also shifts up the energy levels of the nanocrystals, relative to the Fermi level so that heavily n‐doped emitters convert into only slightly n‐doped ones; this boosts the charge injection efficiency of the corresponding light‐emitting diodes. The light‐emitting devices based on those nanocrystals reached a high external quantum efficiency of 29.4 % corresponding to a current efficiency of 123 cd A−1, and showed dramatically improved device lifetime, with a narrow bandwidth of 22 nm and Commission Internationale de I'Eclairage coordinates of (0.20, 0.76) for color‐saturated green emission for the electroluminescence peak centered at 534 nm, thus being fully compliant with the latest standard for wide color gamut displays. [ABSTRACT FROM AUTHOR]

Memristors have received widespread attention as a new type of nonvolatile memory device, which are promising to mimic synapse dynamics efficiently. In this work, a memristor with the structure of PMMA/Ag/FAPbI3/FTO was fabricated and memristive behavior was investigated. With PMMA as the passivation layer in this structure, the performance as well as stability of the FAPbI3 memristor was significantly improved, as compared with non-passivated device. The results show that the device with passivation layer has better stability in the air (20 days) and excellent artificial synaptic functions, such as spike timing-dependent plasticity (STDP), long-term potentiation (LTP) and long-term depression (LTD). This work demonstrates the great potential of PMMA-passivated perovskite memristor in neuromorphic computing. [ABSTRACT FROM AUTHOR]

Hot‐injection methods are widely used for the synthesis of colloidal perovskite nanocrystals (PeNCs). However, the long‐chain hydrocarbon solvents with alkene groups, such as octadecene (ODE), cannot be removed completely due to the strong van der Waals force between ODE and surface ligands as well as the large difference in the polarity with ethyl acetate, which hinders the charge transport characteristic of PeNCs and thus reduces the performance of PeNC‐based light‐emitting diodes (PeLEDs). Herein, an alkene‐free solvent‐assisted strategy is reported to synthesize high‐quality CsPbBr3 PeNCs in toluene and it is found that the alkene‐free solvent can significantly influence the morphology, composition, and optoelectronic properties of PeNCs. Compared to the traditional ODE solvent with alkene groups, toluene endows the higher solubility of precursors, which reduces the growth rate of PeNCs and allows sufficient time for the perovskite crystallization to suppress the bulk defects. Moreover, the similar polarity between toluene and ethyl acetate avoids long‐chain solvent residual on the PeNCs, thereby improving the charge transport characteristics. Making use of these PeNCs prepared with toluene solvent, the resulting PeLEDs present a peak external quantum efficiency of over 15%, 1.5‐fold higher than that of the device based on PeNCs that are prepared in ODE. [ABSTRACT FROM AUTHOR]

1D metal halide perovskites (MHPs) are known as excellent candidates for fabricating high‐performance optoelectronic devices, ranging from lasers to photodetectors (PDs). Nevertheless, their inherent limitations, such as high binding energy and limited carrier mobility, have restricted their further improvement in performance. To tackle this issue, hybrid MHP microwires (MWs) are fabricated by combining MHP MWs and an organic semiconductor via a facile self‐assembly method, forming a radial heterojunction. Meanwhile, an ultrathin insulating organic layer is introduced as an interlayer between MHP MWs and the organic semiconductor. The synthesized hybrid MWs are further applied in rigid and flexible PDs, which demonstrated a high light/dark current on‐off ratio (>2 × 105), a high responsivity (>400 A W−1), and robust bending stability. These impressive results make the hybrid MHP MWs with the unique radial heterostructure promising building blocks for high‐performance future optoelectronics. [ABSTRACT FROM AUTHOR]

Metal halide perovskite light-emitting diodes (PeLEDs) have developed rapidly and achieved tremendous progress in the last few years. However, the performance of blue PeLEDs still lags far behind their red and green counterparts. This review summarizes the optoelectronic properties and preparation methods of blue perovskite materials, proposes the strategies, challenges and perspectives for the further development of blue PeLEDs. [Display omitted] Metal halide perovskites, as a new generation of semiconductor materials, have been widely applied in various optoelectronic devices, especially in the field of perovskite light-emitting diodes (PeLEDs). The external quantum efficiencies (EQEs) of green, red, and near-infrared PeLEDs have exceeded 20% for the last few years, which are comparable to those of the state-of-the-art organic light-emitting diodes (OLEDs) and quantum-dot light-emitting diodes (QLEDs). However, the performances of blue PeLEDs lag far behind those of their counterparts, presumably due to the low quantum yields of blue perovskite films, the instability of the emission spectra, and the difficulties in charge injection for the devices under operation conditions. In this review, the structures and physical properties of blue emissive perovskite materials and the preparation methods of the corresponding perovskite films are firstly addressed. Then, the recent advances and strategies to improve the efficiency of blue PeLEDs are outlined, and the main challenges faced with the blue PeLEDs are also discussed. Finally, an outlook on blue LEDs based on perovskite materials is proposed. [ABSTRACT FROM AUTHOR]

In recent years, impressive progress has been made in developing high‐performance perovskite light‐emitting diodes (PeLEDs) with efficiencies comparable to those of traditional organic light‐emitting diodes (OLEDs). It is convinced that the position of exciton recombination zone is crucial for the performance of the LEDs, however, the dynamics of the exciton recombination zone in PeLEDs and its influence on the performance of PeLEDs remain unclear. Herein, luminescent quantum‐dots (QDs) sensing layers with different energy band landscape and electric properties are introduced into PeLEDs as probers to investigate the position of recombination zone. Consequently, it is found that the band offset between the perovskite layer and the adjacent layer is vital to the position of recombination zone. Modulating the recombination zone towards the bulk of the emission layer helps to improve the device performance as well as the operational stability. [ABSTRACT FROM AUTHOR]

Polarization emission from halide perovskite is expected to bring a lot of benefits for next‐generation displays, such as cost down, wide color gamut, and structure simplification. In this work, strong linearly polarized luminescence from emissive halide perovskites modulated by photoaligned azobenzene dye AD1 is demonstrated. The azobenzene dye functionalized halide perovskite thin films not only exhibit exceptionally high degree of polarization (DOP) of 86.2–93.1% for red, green, and blue emission, but also promise an improved environmental stability originating from the hydrophobic nature of the azobenzene dye. When these perovskite/AD1 composite films are applied in liquid crystal display panels to replace the conventional thick polarizer, the energy efficiency can be doubled and the color gamut can be extended to >120% NTSC. Furthermore, the AD1 functionalized strategy is successfully employed to generate linearly polarized electroluminescence from an inverted perovskite light‐emitting diode, showing a high DOP of 47%. [ABSTRACT FROM AUTHOR]

Electroluminescent devices based on metal halide perovskites have attracted extensive attention owing to their high external quantum efficiency, excellent color purity, and inexpensive solution process. So far, extensive efforts have been made to improve the efficiency of the monochromatic perovskite light‐emitting diodes (LEDs). However, multicolor perovskite‐based LEDs are seldom studied. Here, an individual device capable of multicolor emission in response to the passage of external electric bias is demonstrated. With the rational design of the energy band alignment and control of the carrier transport property, color‐tunable electroluminescent devices based on inorganic halide perovskite and chalcogenide quantum‐dots are fabricated with a wide color tuning range, high color reversibility, and ultrafast color switching. The mechanism of chromaticity tuning is investigated and is explained by the shift of the exciton recombination zone with the driving voltage. The presented work will impact scientific communities by encouraging the manufacture of cost‐effective, high‐resolution, and full‐color displays and human‐centric lighting. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have attracted considerable attention in the field of light‐emitting diodes due to their high color purity and solution processability. However, most perovskite light‐emitting diodes (PeLEDs) employ thermally deposited charge transport layers (CTLs) on top of perovskite layers. In order to realize low‐cost and scalable fabrication of PeLEDs, all‐solution process is highly desired, but still remaining great challenges. Here, an efficient all‐solution‐processed green PeLEDs is reported by incorporating 1,3,5‐tris(1‐phenyl‐1H‐benzimidazol‐2‐yl)benzene (TPBi) doped conjugated amino‐alkyl substituted polyfluorene poly[(9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] (PFN) electron injection layer, achieving a maximum luminance of 9875 cd m−2, a high current efficiency of 10.41 cd A−1, and an external quantum efficiency of 3.19%. Since the solvents used for perovskite precursors and PFN are orthogonal, the protected and complete interface of perovskite film and CTL is effectively obtained by solution processes. The doping of TPBi into PFN not only enhances the capability of electron injection, but also significantly suppresses the emission quenching of perovskite films caused by the charge transfer between perovskite and PFN due to the reduced difference in their work functions. This work provides an efficient approach for the development of all‐solution‐processed PeLEDs. [ABSTRACT FROM AUTHOR]