Exploiting a Multiphase Pure Formamidinium Lead Perovskite for Efficient Green-Light-Emitting Diodes.

Formamidinium (FA)-based perovskites have demonstrated excellent advances in optoelectronics recently, but in terms of perovskite compounds, the optimal condition of their composition optimization remains controversial. Herein, we boosted the performance of perovskite light-emitting diodes (PeLEDs) in both efficiency and stability through composition and phase engineering. The low-dimensional FA2PbBr4 particles emerged and mixed with the FAPbBr3 composites when the FABr content is excessive. By regulating the phase composition in multiphase FAPbBr3 perovskites, the maximum external quantum efficiency (EQEmax) of optimal PeLEDs (5.14%) is 2.7-fold higher than that of pure FAPbBr3-based PeLEDs (1.90%), and device stability is improved. Further optimizing the film quality and emission efficiency with Rb+ ions, the EQEmax of PeLEDs can be increased to 6.01%, with a half-lifetime of about 185 s under the high current density. This strategy of phase composition optimization in FA-based perovskites provides an effective way to process high-efficiency and stable PeLEDs.