Performance Enhancement by ZnO Nanoparticle Layer in Hybrid Ionic Transition Metal Complex-Light-Emitting Electrochemical Cells (iTMC-LECs)

Light-emitting electrochemical cells (LECs) are solution processable solid-state light sources comprising in their simplest architecture an ionic emissive layer in between of two electrodes. Although LECs possess several advantages that make them promising candidates for future large-area low-cost lighting technologies, their device wall-plug efficacies remain so far moderate on the order of a few lumens per watt. One of the reasons therefore is considered to be the charge imbalance within the device. Here, a hybrid LEC device concept is introduced, whereby an additional layer of zinc oxide (ZnO) nanoparticles at the cathode side supports electron injection into the active light-emitting layer and boosts the performance of the Ir-based ionic transition metal complex LEC (iTMC-LEC). The brightness and efficacy of the devices can be increased in average by more than 70% by the implementation of the additional inorganic layer. The time to reach the maximum brightness can be reduced in average by a factor of 7, which is attributed to an improved electron/hole balance in the device due to enhanced electron injection into the active iTMC layer.