Mixed Monoammonium/Diammonium Ligands for High-Efficiency Sky-Blue Quasi-2D Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) metal halide perovskites have demonstrated great potential in light-emitting displays. Monoammonium cation ligands are widely employed for preparing quasi-2D perovskites. Herein, a mixed-ligand strategy combining monoammonium ligand 4-methoxyphenethylammonium hydrobromide with diammonium ligand 3,6-dioxa-1,8-octanediammonium hydrobromide (DADOBr2) is proposed for preparing blue-emissive quasi-2D perovskites. The diammonium ligand of DADOBr2 not only serves as a linker of adjacent inorganic layers to enhance the rigidity of the quasi-2D perovskite structure, but also favors passivating the uncoordinated Pb2+ ions with its oxygen atoms, therefore reducing the energy loss caused by exciton-phonon coupling and trap-assisted nonradiative recombination. It is also found that the mixed-ligand strategy leads to random crystal orientation of quasi-2D perovskites, resulting in restricted carrier transport and increased radiative recombination rate. The mixed-ligand strategy significantly enhances the photoluminescence quantum yield of the blue quasi-2D perovskite film and boosts the external quantum efficiency of the blue device to 14.2%.