Self-assembled hierarchical nanostructured perovskites enable highly efficient LEDs via an energy cascade

Metal halide perovskites have established themselves as extraordinary optoelectronic materials, exhibiting promise for applications in large area illumination and displays. However, low luminescence, low efficiencies of the light-emitting diodes (LEDs), and complex preparation methods currently limit further progress towards applications. Here, we report on a new and unique mesoscopic film architecture featuring the self-assembly of 3D formamidinium lead bromide (FAPbBr(3)) nanocrystals of graded size, coupled with microplatelets of octylammonium lead bromide perovskites, which enables an energy cascade, yielding very high-performance light-emitting diodes with emission in the green spectral region. These hierarchically structured perovskite films exhibit photoluminescence quantum yields of over 80% and LEDs associated with record high efficiencies in excess of 57.6 cd A(-1) with an external quantum efficiency above 13%. Additionally, due to low turn-on voltages (similar to 2.2 V) the LEDs have power efficiencies exceeding 58 lumens per watt, obtained without any light-outcoupling structures.