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

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 cm 2 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.