Nearly 40% outcoupling efficiency in OLEDs with all-metal electrodes

Abstract

Due to its high transparency and low sheet resistance, indium tin oxide (ITO) has been the material of choice for transparent anodes in organic light-emitting diodes (OLEDs). Indium tin oxide, however, is a source of outcoupling loss due to waveguiding and reduced mechanical stability on flexible/stretchable substrates due to its brittle nature. We demonstrate that highly efficient ITO-free OLEDs can be achieved using high quality silver electrodes and horizontally aligned dipole emitters to avoid plasmonic losses. Using an ultrathin Ag/MPTMS anode and a partially aligned phosphorescent emitter, we demonstrate OLEDs with 30% EQE, luminous efficiency exceeding 130 lm/W, and low leakage current. In addition, we demonstrate OLEDs with an optimized structure showing a 36.1% outcoupling efficiency. Theoretical calculations show that our approach can yield up to 48.4% outcoupling efficiency for perfect horizontal alignment, which exceeds the maximum achievable with ITO. The combination of a silver anode and a horizontal phosphorescent emitter is promising for the future design of ultra-efficient flexible OLEDs.