Realizing 8 cd A−1 Current Efficiency for Solution-Processed Inverted Top-Emitting Polymer Light-Emitting Diodes

We report indium tin oxide-free top-emitting organic light-emitting diodes (OLEDs) with solution-processed organic layers. The two electrodes are made of evaporated silver, creating a Fabry-Perot resonator. The main issue of solution-processed OLEDs is the thickness reproducibility, which greatly influences the top-emitting OLED’s performance and color because of the optical resonator. In this work, we combine simulation with experimental results to show the good thickness homogeneity of the spin-coated layers, with a 7% thickness accuracy. Similar efficiencies are obtained for top- and bottom-emitting OLEDs based on the same organic materials, 8.1 ± 0.3 cd A−1 and 8.1 ± 0.2 cd A−1, respectively, with similar Commission Internationale de l’Éclairage (CIE) coordinates. This work demonstrates the feasibility to fabricate microcavity top-emitting OLEDs by solution process and the possibility to increase the performance by using a capping layer.