Homogeneous Phase Distribution in Q-2D Perovskites via Co-assembly of Spacer Cations for Efficient Light-emitting Diodes.

Quasi-2D (Q-2D) perovskites are promising candidates applied in light-emitting diodes (LEDs). However, delicate control on crystallization kinetics is needed to suppress severe phase segregation and wide phase distribution. Here, we investigate the crystallization kinetics of Q-2D perovskites via in-situ absorbance spectroscopy and for the first time find the multiphase distribution is governed by the arrangement, rather than diffusion, of spacer cations at nucleation stage, which associate with its assembling ability determined by molecular configuration. We conceive a "co-assembly" strategy by combining co-cations with different configuration characteristics, where bulky cations disturb the assembling between slender cations and lead-bromide sheet, contributing to homogeneous emitting phase with effective passivation. Correspondingly, in the phenylethylammonium (PEA )-based Q-2D perovskites ( = 3), homogeneous phase distribution is achieved by incorporating co-cation triphenylmethaneammonium (TPMA ), the branching terminals of which suppress cations assembling into low-n phases and afford adequate cations as passivating ligands. Therefore, the champion external quantum efficiency (EQE) of the LED device reach 23.9%, which is among the highest performance of green Q-2D perovskite LEDs. This work reveals that arrangement of spacer cations is key factor that determine the crystallization kinetics in Q-2D perovskites, providing further guidance on the molecular design and phase modulation of Q-2D perovskites. This article is protected by copyright. All rights reserved.