Transformation of Quasi‐2D Perovskite into 3D Perovskite Using Formamidine Acetate Additive for Efficient Blue Light‐Emitting Diodes

Abstract Perovskite films have emerged as candidates for light‐emitting diodes on accounts of excellent optical properties and low cost. Construction of quasi‐2D perovskite films by incorporating organic ammonium is an effective method to manufacture a pinhole‐free film with high photoluminescence quantum yield (PLQY). However, excess organic ammonium hampers carrier mobility through forming insulating capping layer and facilitates the formation of alow‐dimensional perovskite (n = 1 and n = 2) phase that accelerates non‐radiative recombination, resulting in poor performance of light‐emitting diodes. In this work, formamidine acetate is added into the quasi‐2D perovskite to modulate the optical and electrical properties of the perovskite films (CsFA‐Ac). Acetate ions are in favor of washing away excess ammonium and formamidine ions are beneficial to increase the formation energy of low‐dimensional (n = 2) phase. As a result, the quasi‐2D perovskite is transformed into 3D perovskite. The PLQY of the obtained CsFA‐Ac perovskite films is boosted to 59.9% and carrier mobility is enhanced to 47.3 cm² V^‐1 s^‐1. Blue perovskite light‐emitting diode based on the CsFA‐Ac film is endowed with a prominent EQE of 8.8% (average 7.0%) at 477 nm. This work demonstrates a strategy for the development of efficient perovskite light‐emitting diodes.