Mixed-ligands engineering for quasi-2D perovskite toward efficient sky-blue light-emitting diodes
Achieving efficient blue emission with spectra stability by perovskite light-emitting diodes (PeLEDs) is a great challenge, although the external quantum efficiency (EQE) of PeLEDs for red and green emission has exceeded 20%. Here, we reported efficient sky-blue PeLEDs 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 a co-ligand, it is found that molecule size and charge on N atom 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 ligands overloading could be effectively avoided benefiting from the relatively weak coordination ability of DMA due to the relatively small positive charge on N. The optimized PeLEDs based on BA2DMA1.6Cs2Pb3Br11.6 and PEA2DMA1.2Cs2Pb3Br11.2 afford color-stable sky-blue (490 nm) and bluish green (499 nm) emission with a record maximum luminance of 2825 and 7760 cd/m2 respectively. The applicability of this approach in red emission region is also demonstrated, which provides a versatile strategy for full spectra modulation.