Domain Controlling by Compound Additive toward Highly Efficient Quasi‐2D Perovskite Light‐Emitting Diodes

Abstract Quasi‐2D perovskites with enlarged exciton binding energy and tunable bandgap are appealing for application in perovskite light‐emitting diodes (PeLEDs). However, wide n domains distribution is commonly formed in solution‐processed quasi‐2D perovskite films due to the uncontrollable crystallization behavior, which leads to low device performance. Here, the crystallization process is successfully regulated to narrow the n domains distribution by introducing compound additive of ZrO 2 nanoparticles (NPs) and Cryptand complexant. ZrO 2 NPs can avoid the segregation of organic large and small cations by strengthening the solvent extraction capacity of antisolvent, while Cryptand offsets the poor solubility of PbBr 2 by forming an intermediate state to slow down the crystallization of high‐ n domains. Consequently, both high photoluminescence quantum yields over 90% and a high external quantum efficiency of 21.2% are obtained in the optimized green quasi‐2D PeLEDs. Moreover, the lifetime extends about four times compared with control devices. The strategy of domain controlling by compound additive provides a powerful way to develop high‐performance quasi‐2D perovskite optoelectrical devices.