Organometal halide perovskites (OHP) are promising materials for low-cost, high-efficiency light-emitting diodes. In films with a distribution of two-dimensional OHP nanosheets and small three-dimensional nanocrystals, an energy funnel can be realized that concentrates the excitations in highly efficient radiative recombination centers. However, this energy funnel is likely to contain inefficient pathways as the size distribution of nanocrystals, the phase separation between the OHP and the organic phase. Here, we demonstrate that the OHP crystallite distribution and phase separation can be precisely controlled by adding a molecule that suppresses crystallization of the organic phase. We use these improved material properties to achieve OHP light-emitting diodes with an external quantum efficiency of 15.5%. Our results demonstrate that through the addition of judiciously selected molecular additives, sufficient carrier confinement with first-order recombination characteristics, and efficient suppression of non-radiative recombination can be achieved while retaining efficient charge transport characteristics.

All inorganic perovskite nanocrystals (NCs) of CsPbX (X = Cl, Br, I, or their mixture) are regarded as promising candidates for high-performance light-emitting diode (LED) owing to their high photoluminescence (PL) quantum yield (QY) and easy synthetic process. However, CsPbX NCs synthesized by the existing methods, where oleic acid (OA) and oleylamine (OLA) are generally used as surface-chelating ligands, suffer from poor stability due to the ligand loss, which drastically deteriorates their PL QY, as well as dispersibility in solvents. Herein, the OA/OLA ligands are replaced with octylphosphonic acid (OPA), which dramatically enhances the CsPbX stability. Owing to a strong interaction between OPA and lead atoms, the OPA-capped CsPbX (OPA-CsPbX) NCs not only preserve their high PL QY (>90%) but also achieve a high-quality dispersion in solvents after multiple purification processes. Moreover, the organic residue in purified OPA-CsPbBr is only ∼4.6%, which is much lower than ∼29.7% in OA/OLA-CsPbBr. Thereby, a uniform and compact OPA-CsPbBr film is obtained for LED application. A green LED with a current efficiency of 18.13 cd A, corresponding to an external quantum efficiency of 6.5%, is obtained. Our research provides a path to prepare high-quality perovskite NCs for high-performance optoelectronic devices.

Recently, all-inorganic cesium lead halide (CsPbX 3 , X = Cl, Br, I) perovskite nanocrystals have drawn much attention because of their outstanding photophysical properties and potential applications. In this work, a simple and efficient solvothermal approach to prepare CsPbX 3 nanocrystals with tunable and bright photoluminescent (PL) properties, controllable composition, and morphology is presented. CsPbX 3 nanocubes are successfully prepared with bright emission high PL quantum yield up to 80% covering the full visible range and narrow emission line widths (from 12 to 36 nm). More importantly, ultrathin CsPbX 3 (X = Cl/Br, Br, and Br/I) nanowires (with diameter as small as ≈2.6 nm) can be prepared in a very high morphological yield (almost 100%). A strong quantum confinement effect is observed in the ultrathin nanowires, in which both the absorption and emission peaks shift to shorter wavelength range compared to their bulk bandgap. The reaction parameters, such as temperature and precursors, are varied to investigate the growth process. A white light-emitting device prototype device with wide color gamut covering up to 120% of the National Television System Committee standard has been demonstrated by using CsPbBr 3 nanocrystals as the green light source. The method in this study provides a simple and efficient way to prepare high-quality CsPbX 3 nanocrystals.The ORCID identification number(s) for the author(s) of this article can be found under http://dx.doi.org/10.1002/adfm.201701121.light-emitting devices (LEDs), [3] fieldeffect transistors, [4] solar cells, [5] and so on. Although much progress has been made in the preparation of traditional colloidal semiconductor nanocrystals, the current synthetic strategies are still suffering from several challenges, including low yield, complex procedures, and toxic chemicals. It is thus highly desired to develop new types of semiconductor nanocrystals that possess excellent photoluminescent properties and can be prepared in a simple, reproducible, and cost-effective way. For this purpose, recently, a new family of perovskite semiconductor nanocrystals has proven to be a great candidate for optoelectronic applications due to their low cost, easy preparation, high reproducibility, and great photoluminescent properties. [6] For example, the organic-inorganic hybrid perovskite, i.e., CH 3 NH 3 PbX 3 (X = Cl, Br, I), have been used in solar cell and showed great performance. [7] However, the hybrid perovskite nanocrystals are highly sensitive to moisture and oxygen, resulting in low stability. Since the pioneered work by Kovalenko and co-workers in 2015, intensive research efforts have been devoted to studying the all-inorganic cesium lead halide (CsPbX 3 , X = Cl, Br, I) perovskite nanocrystals, which show outstanding photophysical properties, including composition-and size-controlled photoluminescent property, high PL quantum yield (PLQY), narrow emission widths, and short radiative lifetime. [8] The all-inorganic perovskite nanocrystals have been prepared through...

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All-inorganic perovskite light-emitting diodes (LEDs) reveal efficient luminescence with high color purity, but their modest brightness and poor stability are still critical drawbacks. Here, the luminescent efficiency and the stability of perovskite LEDs (PeLEDs) are boosted by antisolvent vapor treatment of CsPbBr 3 embedded in a dielectric polymer matrix of polyethylene oxide (PEO). A unique method is developed to obtain high quality CsPbBr 3 emitting layers with low defects by controlling their grain sizes. CsPbBr 3 in PEO matrix is post-treated with antisolvent of chloroform (CF), leading to microcrystals with a size of ≈5 µm along the in-plane direction with active emitting composite of 90%. A device based on CF post-treatment (CsPbBr 3 -PEO-CF) film displays a brightness of up to 51890 cd m −2 with an external quantum efficiency of 4.76%. CsPbBr 3 -PEO-CF PeLED still maintains 82% of its initial efficiency after 80 h continuous operation in ambient air, which indicates relatively good device stability. This work highlights that film quality is not only key to promoting fluorescence in CsPbBr 3 , but also to achieving higher performance PeLEDs.

Defect passivation has been demonstrated to be effective in improving the radiative recombination of charge carriers in perovskites, and consequently, the device performance of the resultant perovskite light‐emitting diodes (LEDs). State‐of‐the‐art useful passivation agents in perovskite LEDs are mostly organic chelating molecules that, however, simultaneously sacrifice the charge‐transport properties and thermal stability of the resultant perovskite emissive layers, thereby deteriorating performance, and especially the operational stability of the devices. We demonstrate that lithium halides can efficiently passivate the defects generated by halide vacancies and reduce trap state density, thereby suppressing ion migration in perovskite films. Efficient green perovskite LEDs based on all‐inorganic CsPbBr3 perovskite with a peak external quantum efficiency of 16.2 %, as well as a high maximum brightness of 50 270 cd m−2, are achieved. Moreover, the device shows decent stability even under a brightness of 104 cd m−2. We highlight the universal applicability of defect passivation using lithium halides, which enabled us to improve the efficiency of blue and red perovskite LEDs.

A fast and efficient microwave-assisted strategy is developed to prepare high-quality CsPbX3 nanocrystals with controllable morphologies (nanoplate, nanocube, and nanorod).

To improve the efficiency of CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) based light-emitting diodes (LEDs), several parameters should be taken into consideration, including outstanding photophysical properties, efficient charge injection/transporting properties, and suitable device structure. In traditional synthesis of CsPbX3 nanocrystals, oleic acid and oleylamine are widely used as ligands, which require a complicated cleaning step to remove extra residual insulating ligands. In this work, monodisperse CsPbBr3 nanorods with tunable aspect ratio and a clean surface have been prepared through an interfacial conversion from Cs4PbBr6 nanocrystals. The formation process has been carefully investigated. The nanorods showed excellent photophysical properties, including a photoluminescence quantum yield up to 87% and a photoluminescence lifetime of 44 ns. According to the ultraviolet photoelectron spectroscopy measurement, CsPbBr3 nanorods show a higher valence band maximum than that of nanocubes, suggesting a more efficient hole injection rate that is favorable for LED applications. A prototype LED has been fabricated by using CsPbBr3 nanorods as green light source. Without any tedious cleaning step, the external quantum efficiency of the LEDs is over 8.2%, which is one of the best performances of CsPbBr3 NCs-based LEDs so far. This work not only provides a great candidate for high-performance LEDs but also sheds some light on the materials synthesis and device design.