Phase distribution management for high-efficiency and bright blue perovskite light-emitting diodes

Quasi-two-dimensional (quasi-2D) perovskite materials have attracted significant attention for application in light-emitting diodes (PeLEDs) due to their unique optical characteristics and extraordinary performance. The inherent multi-quantum well structure will generate a strong quantum confinement effect which is beneficial for the blue emission. However, the efficiency and stability of the quasi-2D blue PeLEDs lag behind their red and green counterparts, which prevents the further commercial application of the PeLEDs. The performance of quasi-2D blue PeLEDs was limited on account of the inefficient phase distribution management, which causes an inefficient energy transfer and severe non-radiative recombination. Herein, we employ guanidine thiocyanate (GASCN) as the pre-deposited film at the bottom of the perovskite film to manage the phase distribution of the PBA2Csn−1PbnBr3n+1 quasi-2D perovskite film (where n is the number of [PbBr6]4- sheets, and PBA is phenylbutylammonium). The pre-deposited GASCN can not only inhibit the small n-phase (i.e., n = 1: PBA2PbBr4, and n = 2: PBA2CsPb2Br7) but also avoid the undesired emission redshift from the over-growth of the large n-phase as well as passivate defects of the quasi-2D perovskite film, which accelerates energy transfer efficiently, strengthens the carrier transport, and enhances the luminous efficiency. As a result, the optimized device demonstrated the highest external quantum efficiency (EQE) of 16.40% and a maximum luminance of 8290 cd m−2. This strategy provides a new pathway to accurately manage phase distribution of quasi-2D perovskite achieving the high efficiency in blue PeLEDs.