Although perovskite light-emitting diodes (PeLEDs) have recently experienced significant progress, there are only scattered reports of PeLEDs with both high efficiency and long operational stability, calling for additional strategies to address this challenge. Here, we develop perovskite-molecule composite thin films for efficient and stable PeLEDs. The perovskite-molecule composite thin films consist of in-situ formed high-quality perovskite nanocrystals embedded in the electron-transport molecular matrix, which controls nucleation process of perovskites, leading to PeLEDs with a peak external quantum efficiency of 17.3% and half-lifetime of approximately 100 h. In addition, we find that the device degradation mechanism at high driving voltages is different from that at low driving voltages. This work provides an effective strategy and deep understanding for achieving efficient and stable PeLEDs from both material and device perspectives.

Despite quick development of perovskite light‐emitting diodes (PeLEDs) during the past few years, the fundamental mechanisms on how ion migration affects device efficiency and stability remain unclear. Here, it is demonstrated that the dynamic redistribution of mobile ions in the emissive layer plays a key role in the performance of PeLEDs and can explain a range of abnormal behaviours commonly observed during the device measurement. The dynamic redistribution of mobile ions changes charge–carrier injection and leads to increased recombination current; at the same time, the ion redistribution also changes charge transport and results in decreased shunt resistance current. As a result, the PeLEDs show hysteresis in external quantum efficiencies (EQEs) and radiance, that is, higher EQEs and radiance during the reverse voltage scan than during the forward scan. In addition, the changes on charge injection and transport induced by the ion redistribution also well explain the rise of the EQE/radiance values under constant driving voltages. The argument is further rationalized by adding extra formamidinium iodide (FAI) into optimized PeLEDs based on FAPbI3, resulting in more significant hysteresis and shorter operational stability of the PeLEDs.

Bandgap tuning through mixing halide anions is one of the most attractive features for metal halide perovskites. However, mixed halide perovskites usually suffer from phase segregation under electrical biases. Herein, we obtain high-performance and color-stable blue perovskite LEDs (PeLEDs) based on mixed bromide/chloride three-dimensional (3D) structures. We demonstrate that the color instability of CsPb(Br 1– x Cl x ) 3 PeLEDs results from surface defects at perovskite grain boundaries. By effective defect passivation, we achieve color-stable blue electroluminescence from CsPb(Br 1– x Cl x ) 3 PeLEDs, with maximum external quantum efficiencies of up to 4.5% and high luminance of up to 5351 cd m –2 in the sky-blue region (489 nm). Our work provides new insights into the color instability issue of mixed halide perovskites and can spur new development of high-performance and color-stable blue PeLEDs.

Metal halide perovskites have demonstrated impressive properties for achieving efficient monochromatic light-emitting diodes. However, the development of white perovskite light-emitting diodes (PeLEDs) remains a big challenge. Here, we demonstrate a...

applications in optical and electronic devices, such as light-emitting diodes (LEDs), [2] solar cells, [3] quantum communications elements, [4] and thermoelectrics. [5] In general, semiconductor QDs can be obtained through epitaxial [5] or colloidal [2] growth, using vapor phase and chemical reactions, respectively. In contrast to the epitaxial QDs, colloidal QDs are solution-processable semiconductors. Such materials are compatible with light-weight and flexible plastic substrates and carry promise for future low-cost and large-area optoelectronic devices. [6] In particular, colloidal QDs have easily tunable emission, narrow emission bandwidth, and high photoluminescence (PL) efficiency, making them ideal candidates for LEDs. [7] Since the first demonstration in 1994, [8] colloidal QD LEDs have realized major advances, currently reaching external quantum efficiencies (EQEs) over 20%. [9,10] Recently, metal halide perovskites have emerged as promising solutionprocessable semiconductors, competitive with the best inorganic semiconductors such as silicon and gallium arsenide. [11] They are not only strong light absorbers with excellent semiconducting properties for solar cells, but also promising light-emitting materials with high PL efficiency, narrow and easily tunable emissive line shapes, and wide color gamut. [12] Since the pioneering work on room-temperature perovskite LEDs was reported in 2014, [13] Semiconductor quantum dots (QDs) are among the most promising nextgeneration optoelectronic materials. QDs are generally obtained through either epitaxial or colloidal growth and carry the promise for solutionprocessed high-performance optoelectronic devices such as light-emitting diodes (LEDs), solar cells, etc. Herein, a straightforward approach to synthesize perovskite QDs and demonstrate their applications in efficient LEDs is reported. The perovskite QDs with controllable crystal sizes and properties are in situ synthesized through one-step spin-coating from perovskite precursor solutions followed by thermal annealing. These perovskite QDs feature size-dependent quantum confinement effect (with readily tunable emissions) and radiative monomolecular recombination. Despite the substantial structural inhomogeneity, the in situ generated perovskite QDs films emit narrow-bandwidth emission and high color stability due to efficient energy transfer between nanostructures that sweeps away the unfavorable disorder effects. Based on these materials, efficient LEDs with external quantum efficiencies up to 11.0% are realized. ThisThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.201804947.One of the most attractive properties of semiconductor quantum dots (QDs) is a remarkable change of optical properties as a function of the crystal size. [1] In principle, their electronic transitions shift to higher energy with decreasing crystal dimensions, well known as the size-dependent quantum confinement effect. This property makes QDs attractive for the Small 20...

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