Spacer Cation Engineering Enables Blue Quasi‐2D Perovskites to Achieve Highly Efficient and Spectrally Stable Electroluminescence

Abstract

Abstract The combination of organic spacer cations and mixed‐halides to produce multiphase quasi‐2D perovskites is a promising strategy for fabricating blue perovskite light‐emitting diodes (PeLEDs). However, insufficient energy transfer, trap‐assisted recombination and exciton‐phonon coupling lead to significant non‐radiative losses. Here, a co‐spacer engineering strategy of binding guanidinium (GA + ) and ortho ‐fluorophenylethylamium (oF‐PEA + ) through hydrogen bonds is proposed to prepare blue mixed‐halide quasi‐2D perovskite films with high photoluminescence quantum yields (PLQYs). GA + with Lewis base characteristics reduces the trap states by defect passivation. Additionally, oF‐PEA + inhibits the rapid diffusion of GA + by hydrogen bonding interactions, which mitigates the formation of undesirable low‐dimensional phases and facilitates the growth of high‐dimensional emissive phases with a more concentrated distribution, resulting in efficient energy transfer of excitons and weaker exciton‐phonon coupling. These synergistic effects enable the blue perovskite films to achieve a PLQY as high as 91.5%. As a result, the fabricated blue PeLEDs show a remarkable external quantum efficiency of 21.1% at the stable emissionpeak of 489 nm with a narrow full width at half‐maximum of 19 nm.