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Inkjet‐printed perovskite quantum dot (PQD) color conversion films (CCFs) have great potentials for mini/micro‐LED displays because of their ultrahigh color purity, tunable emissions, high efficiency, and high‐resolution. However, current PQD inks mainly use expensive, toxic, and flammable organic substances as solvents. In this work, water is proposed to be used as the solvent for inkjet printing PQD/polymer CCFs. The green‐emitting patterned MAPbBr3/polyvinyl alcohol (PVA) films are in situ prepared by using halides and the PVA‐based aqueous ink. The as‐printed CCFs exhibit a high‐resolution dot matrix of 90 µm with a bright green emission (λem = 526 nm), a high photoluminescence quantum yield of 85%, and a narrow full width at half maximum of 22 nm. They have both air‐ and photo‐stabilities under ambient conditions, and each pixel of CCFs is relatively uniform in morphology and fluorescence when the substrate temperature is 80 °C. The patterned blue‐emitting MAPbClxBr3‐x/PVA and red‐emitting Cs0.3MA0.7PbBrxI3‐x/PVA can also be printed by aqueous inks. These results indicate that the designed aqueous inks are promising for in situ inkjet printing high resolution and reliability PQD CCFs for mini/micro‐LED displays.

Perovskite light‐emitting diodes (PeLEDs) are strong candidates for next‐generation display and lighting technologies due to their high color purity and low‐cost solution‐processed fabrication. However, PeLEDs are not superior to commercial organic light‐emitting diodes (OLEDs) in efficiency, as some key parameters affecting their efficiency, such as the charge carrier transport and light outcoupling efficiency, are usually overlooked and not well optimized. Here, ultrahigh‐efficiency green PeLEDs are reported with quantum efficiencies surpassing a milestone of 30% by regulating the charge carrier transport and near‐field light distribution to reduce electron leakage and achieve a high light outcoupling efficiency of 41.82%. Ni0.9Mg0.1Ox films are applied with a high refractive index and increased hole carrier mobility as the hole injection layer to balance the charge carrier injection and insert the polyethylene glycol layer between the hole transport layer and the perovskite emissive layer to block the electron leakage and reduce the photon loss. Therefore, with the modified structure, the state‐of‐the‐art green PeLEDs achieve a world record external quantum efficiency of 30.84% (average =  29.05 ± 0.77%) at a luminance of 6514 cd m−2. This study provides an interesting idea to construct super high‐efficiency PeLEDs by balancing the electron‐hole recombination and enhancing the light outcoupling.

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The room-temperature ligand-assisted reprecipitation (LARP) technique has been established as a facile and large-scale method for synthesizing lead halide perovskite nanocrystals (PNCs). However, it is difficult to purify these PNCs through precipitation/redispersion processes, arising from their fragile crystal structure and low PNC concentration. In this paper, we proposed to apply anisole as the reaction solvent, which has slightly increased polarity relative to the often used toluene. As a result, the as-synthesized CsPbBr 3 PNCs can be easily isolated from the crude solution through direct centrifugation without adding antisolvents. The obtained purified CsPbBr 3 (OA/OAm-CsPbBr 3 ) PNCs capped with oleic acid (OA) and oleylamine (OAm) had a 50-fold improvement in molar production yields. Meanwhile, they showed a relatively high photoluminescence quantum yield (PLQY) of 64%. This method is also feasible for more fragile red-emitting PNCs. The obtained CsPbBrI 2 PNCs with an emission maximum at 629 nm had a PLQY of 65% and a 7-fold improvement in molar production yields. Furthermore, when bromide-rich ligands [i.e., cetyltrimethylammonium bromide (CTAB)] were used, the PLQY of the purified CsPbBr 3 (CTAB-CsPbBr 3 ) PNCs can further increase to around 90%. Subsequently, for facile coating PNCs with polystyrene (PS), a mild polymerization method was established by adopting a low-temperature initiator. The fabricated CTAB-CsPbBr 3 @PS composite had a higher PLQY (77% vs 21%) and enhanced stability against water and heat, compared to that of the OA/OAm-CsPbBr 3 @PS composite. Finally, the CTAB-CsPbBr 3 @PS composite was demonstrated to produce super-wide color gamut (130% NTSC) backlights with a luminous efficacy of 71.1 lm/W.