In this study, a low-temperature method was adopted to synthesize all-inorganic cesium lead bromide CsPbBr3 nanocrystals (NCs) as the active layer in light-emitting devices. To improve the film-forming and optoelectronic properties of the CsPbBr3 NCs, a surface ligand diphenylammonium bromide (DPABr) was added in the range from 0 to 0.15 mole fraction in proportion to the amount of oleylamine. The experimental results showed that introducing 0.1 mole fraction of DPABr in the CsPbBr3 NCs achieved the best performance. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) results revealed that smooth and pinhole-free films of the CsPbBr3 NCs were formed by introducing DPABr with a low surface roughness of 4.6 nm. The introduced bromide ions can passivate the surface vacancies of the CsPbBr3 NCs and improve the photoluminescence quantum yield (PLQY) from 38 to 72% compared with that of the pristine CsPbBr3 NCs. Moreover, shorter and π-electron-rich phenyl groups help to increase carrier injection into the nanocrystalline core, preventing the carriers from being hindered by oleic acid and oleylamine with longer alkyl chains. Therefore, the conductivity of the resulting CsPbBr3 NCs was augmented. The maximum brightness and the current efficiency of the optimized device based on the CsPbBr3 NCs with 0.1 mole fraction of DPABr were enhanced 2.3- and 3.3-fold, respectively, relative to those of the pristine one.