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Barrier-free injections of electrons and holes, followed by effective confinement and radiative recombination of charge carriers, are critical for electroluminescent devices. Here, we utilize a structure of ITO/polyethyleneimine (PEI) modified ZnO/organometal halide perovskite/poly(9,9-dioctyl-fluorene-co-N-(4-butylpheny l)diphenylamine) (TFB)/MoOx/Au for highly efficient electroluminescence. We demonstrate that the PEI modified ZnO affords a low work-function cathode for ohmic electron injection and provides a high-energy hydrophilic surface that gives good perovskite film formation from solution. Green-emitting CH3NH3PbBr3 perovskite LEDs (PeLEDs) with a luminous efficacy of ~4.0 lm W-1 at a luminance of ~20,000 cd m-2 are achieved.