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 PbBr64– octahedra passivation strategy to achieve a 96% absolute QY for the ultrapure (line width = 12 nm) blue emission from CsPbBr3 nanoplatelets (NPLs), and both values rank first among perovskite NCs with blue emission. From the aspect of constructing intact PbBr64– 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.

In Situ Passivation of PbBr64– Octahedra toward Blue Luminescent CsPbBr3 Nanoplatelets with Near 100% Absolute Quantum Yield