Mixed-Ligands Perovskite Material For Blue Emission And Its Application In Light-emitting Diodes

Achieving efficient blue emission with spectra stability by perovskite light-emitting diodes(Pe LEDs)is a great challenge,although the external quantum efficiency(EQE)of Pe LEDs for red and green emission has exceeded 20%.Here,we reported efficient sky-blue Pe LEDs with high brightness based on mixed-ligands confined quasi-2D perovskite.By detailed characterization of the optical and physicochemical properties of n-butylammonium(BA)or 2-phenylethylammonium(PEA)-based perovskite with various of alkyl ammonium bromide as co-ligand,it is found that molecule size and charge on amino-groups of the co-ligand hold the keys to constructing effective mixed-ligands system.Accordingly,dimethylammonium(DMA)is an ideal co-ligand in both BA-and PEA-based quasi-2D perovskite.Thanks to its proper molecular size,DMA could help to confine the diameter of perovskite nanocrystals(NCs)and improve their dispersity in organic ligands.Besides,the phase of n=1 caused by excess ligands could be effectively avoided benefiting from the relatively weak coordination ability of DMA due to the relatively small positive charge on amino-groups.The optimized Pe LEDs based on BA₂DMA_1.6Cs₂Pb₃Br_11.6 and PEA₂DMA_1.2Cs₂Pb₃Br_11.2 afford color-stable sky-blue(490 nm)and bluish green(499nm)emission with a record maximum luminance of 2825 and 7759 cd/m²respectively.Besides,this method is applicable to mixed anionic perovskite systems.A standard blue light emission of 460 nm is achieved.The surface defects could be passivated by the co-ligand(DMABr)hence resulting in blue-shifted PL with enhanced QY.A PLQY of 38.8%at 476 nm is achieved.This universal method provides a new idea for adjusting the spectrum,and can be adjusted in the blue and red light range.It has the potential for full spectrum adjustment and can be used simultaneously with other methods.