Improvement of device performance of solution-processed multilayered LEDs with QD/polymer blend as the emission layer

Abstract We fabricated the solution-processed multilayered light-emitting diodes having the colloidal quantum dots/ polymer blend as an emitting layer (QD-LEDs) with the inverted organic LED structure. We proposed the multilayered electron injection layers consisting of 4,7-Dimethoxy-1,10-phenanthroline (p-MeO-Phen) on ZnO nanoparticles, and the multilayers of ZnO:p-MeO-Phen blend (1 st EIL) and the heat-treated Zr (IV) acetylacetonate (Zr(acac) 4 ) as a 2 nd EIL. We achieved a higher material utilization rate and multilayered structure by combining the meniscus coating and transfer printing techniques. We then fabricated the QD-LEDs consisting of ITO/ZnO or ZnO:p-MeO-Phen blend (1st EIL)/2nd EIL/QD: polymer blend/polyvinylcarbazole (PVCz)/Poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) (TFB)/hole injection layer/Anode (Al or Ag). We compared the device performance of QD blended with PVCz and polymethylmethacrylate (PMMA). The thickness of the QD layer was controlled between 1 and 3 QD layers by repeating the meniscus coating and transfer printing. The work function of ZnO was reduced by p-MeO-Phen and the threshold voltage was reduced from 4.9 V to 2.95 V. The peak value of EQE was improved from 1.14% to 3.1% by insertion of Zr(acac) 4 probably owing to the reduction of leakage current and exciton quenching.