Triangular-shaped zinc oxide nanoparticles enhance the device performances of inverted OLEDs

Abstract

Three-fold increase in the efficiencies of inverted bottom-emission organic light emitting diodes (IBOLEDs) is achieved with triangular-shaped zinc oxide nanoparticles (ZnO NPs) synthesized in methanol. ZnO nanoparticles with a diameter ranging from 5 to 10 nm are deposited by a solution process and used as an electron injecting layer (EIL). Influences of the process conditions on device performances such as concentration, annealing temperature and solvents are investigated. IBOLEDs are fabricated with ITO/ZnO NPs/polymer/V<inf>2</inf>O<inf>5</inf>/Al layout where poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) is used as an active layer. The highest brightness and luminous efficiency reaching 1340 cd m-2 and 0.65 cd A-1 are achieved with 2.5% wt triangular-shaped ZnO NPs synthesized in methanol. On the other hand, performances of the devices fabricated with ZnO NPs synthesized in isopropanol (IPA) and ethanol were 723 cd m-2/0.22 cd A-1 and 67 cd m-2/0.011 cd A-1, respectively. © 2015 Elsevier B.V., All rights reserved.