Efficient Electron Injection by Size- and Shape-Controlled Zinc Oxide Nanoparticles in Organic Light-Emitting Devices
Yong-Jin Pu1, Norito Morishita1, Takayuki Chiba1
1Department of Organic Device Engineering, ‡Department of Chemistry and Chemical Engineering, Yamagata University , 4-3-16 Jonan, Yonezawa 992-8510, Japan.
Abstract:
Three different sized zinc oxide (ZnO) nanoparticles were synthesized as spherical ZnO (S-ZnO), rodlike ZnO (R-ZnO), and intermediate shape and size ZnO (I-ZnO) by controlling the reaction time. The average sizes of the ZnO nanoparticles were 4.2 nm × 3.4 nm for S-ZnO, 9.8 nm × 4.5 nm for I-ZnO, and 20.6 nm × 6.2 nm for R-ZnO. Organic light-emitting devices (OLEDs) with these ZnO nanoparticles as the electron injection layer (EIL) were fabricated. The device with I-ZnO showed lower driving voltage and higher power efficiency than those with S-ZnO and R-ZnO. The superiority of I-ZnO makes it very effective as an EIL for various types of OLEDs regardless of the deposition order or method of fabricating the organic layer, the ZnO layer, and the electrode.
