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

• The device characteristics of the inverted bottom-emission organic light emitting diodes (IBOLEDs) containing ZnO nanoparticles (ZnO NPs) used as an electron injecting layer were studied.
• ZnO particles were synthesized in different conditions resulting in different shapes.
• It is found that triangular-shaped ZnO NPs enhanced the device performances of the IBOLEDs.
• Three-fold increase in the efficiencies of IBOLEDs is achieved by using these ZnO NPs.

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/V2O5/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. Through this work, it is found that for the performances of the devices, shape effect is more important than the size.

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