High Efficiency Quantum Dot Light-Emitting Diode by Solution Printing of Zinc Oxide Nanoparticles.

Quantum dot light-emitting diodes (QLEDs) have attracted considerable attention owing to the narrow emission spectra, wide color gamut, high quantum yield and size-controlled emission wavelength. Zinc oxide nanoparticles have been widely used as an electron transport layer (ETL) in QLEDs due to their excellent electrical properties. In this study, we compared the efficiency of QLEDs with organic and zinc oxide ETLs in viewpoint of the charge balance. The QLEDs were constructed using ZnO nanoparticles with an average particle size of 3 nm or 3TPYMB as the ETL materials. CdSe/ZnS quantum dots and poly-TPD were used as a light-emitting elements and hole transporting material, respectively. The QLED with 3TPYMB ETL exhibited current efficiency of 7.71 cd/A, while the efficiency of the QLED using ZnO nanoparticles was significantly improved to 38.76 cd/A. Such a substantial improvement of emission efficiency in the QLEDs with ZnO ETL was attributed to the much better charge balance by the ZnO.