Recently, the pursuit of high photoluminescence quantum yields (PLQYs) for blue emission in perovskite nanocrystals (NCs) has attracted increased attention because the QY of blue NCs lags behind those of green and red ones severely, which is fatal for three-primary-color displays. Here, we propose an in situ PbBr 6 4− octahedra passivation strategy to achieve a 96% absolute QY for the ultrapure (line width = 12 nm) blue emission from CsPbBr 3 nanoplatelets (NPLs), and both values rank first among perovskite NCs with blue emission. From the aspect of constructing intact PbBr 6 4− octahedra, additional Br − was introduced to drive the ionic equilibrium to form intact Pb−Br octahedra. The reduced Br vacancy and inhibited nonradiative recombination processes are well proved by reduced Urbach energy, increased Pb−Br bonds, and slower transient absorption delay. Blue light-emitting diodes (LEDs) using NPLs were fabricated, and a high external quantum efficiency (EQE) of 0.124% with an emission line width of ∼12 nm was realized. This work will provide good references to break the "blue-wall" in perovskite NCs.

efficient inkjet-printed QLEDs as well as the other solutionprocessed electronic devices in the future.

Understanding the subtle structure–property relationships of quantum dots (QDs) is essential for targeted modulation of optoelectronic properties, and the influences of surface defects of inorganic halide perovskite (HP) QDs are still not very clear. Here, the negative exciton trapping effects of surface halide vacancies (VX) on the photoluminescence quantum yield QY (PLQY) of HPQDs are determined by a detailed analysis of the optical parameters, exciton dynamics, and surface chemical states. Based on the fact that VX contribute greatly to nonradiative recombination processes, versatile in situ and postpassivation strategies are developed by constructing intact Pb–X octahedrons. High QYs for standard red CsPbBr1I2 (85%), green CsPbBr3 (96%), and blue CsPbBr1.3Cl1.7 (92%) emissions are achieved. The superiorities of the reduced VX are further demonstrated by high external quantum efficiency of 0.8% and a stable emission wavelength of the blue light‐emitting diodes. This study deepens the understanding of HPQDs and demonstrates the potential for the artificial control of the optical properties of HPQDs.

According to the thinner emitting layer and stronger electric field in perovskite light‐emitting diodes (PeLEDs) than those in perovskite solar cells, the strong electric‐field‐driven ion‐migration is a key issue for the operational stability of PeLEDs. Here, a methylene‐bis‐acrylamide cross‐linking strategy is proposed to both passivate defects and suppress ion‐migration with an emphasis on the suppressing mechanism via in situ investigations. As typical results, in addition to the enhanced external quantum efficiency (EQE, 16.8%), PeLEDs exhibit preferable operational stability with a half lifetime (T50) of 208 h under continuous operation with an initial luminance of 100 cd m−2. Moreover, the EQE of cross‐linked LEDs can maintain above 15% during 25 times scanning as the devices are measured every 4 days. To the authors’ knowledge, this is the highest stability published until now for high‐efficiency PeLEDs with EQE over 15%. The in situ/ex situ mechanism investigation demonstrates that such cross‐linking increases binding energy from 0.54 to 0.92 eV and activation energy from 0.21 to 0.5 eV. Hence, it suppresses ligands breaking away and ion migration, which prevents ions from moving inside and across crystals. The proposed cross‐linking passivation strategy thus provides an effective methodology to fabricate stable perovskites‐based photoelectric devices.

No abstract