Morphological and optoelectronic investigations of CsPbBr3 nanocrystals chelating diphenylammonium halide ligands via low temperature synthesis

The low temperature method was adopted to synthesize all-inorganic cesium lead bromide CsPbBr3 nanocrystals (NCs) as the active layer in light-emitting devices. In order to improve film-forming and optoelectronic properties of CsPbBr3 NCs, a surface ligand diphenylammonium bromide (DPABr) was added 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 CsPbBr3 NCs brought the best performance. The SEM and AFM results revealed that smooth and pinhole-free films of 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 CsPbBr3 NCs and improve photoluminescence quantum yield (PLQY) from 38% to 72% compared with the pristine CsPbBr3 NCs. Moreover, shorter and π electron-rich phenyl groups help to increase carrier injection into nanocrystalline core, preventing 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 current efficiency of the optimized device based on CsPbBr3 NCs with 0.1 mole fraction of DPABr were enhanced 2.3- and 3.3-fold, respectively, relative to the pristine one.