In Situ Controlled Growth of Strongly Quantum Confined CsPbBr3/FAPbBr3 Core/Crown Nanoplatelets for Blue Light Emitting Diodes

Abstract A few unit cells of thick colloidal CsPbBr 3 nanoplatelets (NPLs) exhibit strong quantum confinement. However, due to the increased surface‐to‐volume ratio, they show poor photoluminescence quantum yield (PLQY) resulting from surface traps. Here, a unique, quantum‐confined core/crown perovskite is reported for the first time, where the CsPbBr 3 NPL surface is passivated by laterally grown thin FAPbBr 3 crown layers. Unlike regular core/shells, the FAPbBr 3 is coated around the core NPLs resulting in blue emission. Careful control of the growth kinetics while monitoring growth using in situ PL led to the formation of core/crown perovskites with nearly two times improvement in thin film PLQYs. HR‐TEM analyses show that the interplanar distances of the core match with CsPbBr 3 and the crown match with FAPbBr 3 . The XRD and TEM analyses revealed that their thickness remains the same even if Cs + to FA + ratios are varied, indicating lateral growth of FAPbBr 3 around the CsPbBr 3 core. Further, FA + ions in the crown lattice are confirmed by FTIR and 1 HNMR. Finally, considering their high PLQYs and narrow linewidths, the core/crown NPLs are employed as blue emitters in light‐emitting diodes, and a maximum external quantum efficiency of 0.4% at 2.71 eV (457 nm) with a luminance of 513 cd m −2 is achieved.