Outcoupling efficiency of organic light emitting diodes and the effect of ITO thickness

Outcoupling efficiency of bottom emission organic light emitting diodes (OLEDs) have been analyzed using a model (Adv. Chem. Phys. 37 (1987) 1, [17]) based on classical electromagnetic theory with a full vectorial approach. The analyses presented in this study take into account many factors, including the thickness of the ITO layer. Maximum outcoupling efficiencies over 27% and 30% are achievable if thin ITO layers in the range of 50–70 nm and 50–100 nm are used for blue and green phosphorescent OLEDs, respectively. Even higher efficiencies of 29% for the blue and 31.6% for the green OLED can be obtained if we use thicker organic layers supporting two antinodes suggesting that phosphorescent OLEDs can have a much higher external quantum efficiency than 20%.