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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]

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]

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]