Cesium azide (CsN3) doped 2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (NBphen) has been demonstrated as an efficient electron-injection layer (EIL) in this work. Advantageous for its low evaporation temperature and air stability, CsN3 is employed as an n-dopant to replace the reactive alkali metals or alkali metal compounds. Organic light-emitting diodes utilizing this composite EIL exhibit highly improved current density–luminance–voltage characteristics compared to the control device with LiF. When C545T-doped Alq3 is used as an emitting layer, a maximum current efficiency of 10.4 cd A−1 can be reached. Our results indicate that this CsN3-doped NBphen composite layer has great potential as an alternative EIL in organic electronic devices.