Improved performance of quantum dot light-emitting diodes by hybrid electron transport layer comprised of ZnO nanoparticles doped organic small molecule

Abstract ZnO nanoparticles (NPs) are widely employed as the electron transport layer (ETL) material in quantum dot light-emitting diodes (QLEDs) due to their excellent electron transport properties and inherent stability. However, the unbalanced carrier injection caused by the redundant electron injection is a common phenomenon existing in QLEDs with ZnO ETL. Here, based on the lower electron mobility and shallower lowest unoccupied molecular orbit (LUMO) of most organic electron transport ·materials than ZnO NPs, we report a strategy to modulate the electron transporting properties of ZnO NPs by doping organic small molecular electron transport materials. Several kinds of small molecular dopants including LiQ (lithium 8-quinolate), TPBi (1,3,5-tris(N-phenylbenzimidazol-2,yl) benzene), and BPhen (4,7-diphenyl-1,10-phenanthroline) are separately introduced to modify ZnO. The resulting device with LiQ-doped ZnO ETL at a doping ratio of 7 wt% exhibits the optimal performance at peak current efficiency (CE) and external quantum efficiency (EQE) up to 8.07 cd/A and 7.74%, which are about 1.93- and 1.94-fold higher than 4.19 cd/A and 3.98% of the device with pristine ZnO ETL, respectively. The improvement of performances can be mainly attributed to the inhibition of electron injection and interfacial exciton quenching by the use of LiQ-doped ZnO ETLs. This work may offer a promising method for fabricating high performance QLEDs and promote their application development in the display fields.