Light Emission Mechanism

This chapter describes the light emission mechanisms of OLEDs. There are three common types of emission mechanisms: fluorescent OLED, phosphorescent OLED, and thermally activated delayed fluorescent (TADF) OLED.In the fluorescent OLED, only the excited singlet state gives an emission. The theoretical maximum internal quantum efficiency is only 25%. However, the phosphorescent OLED can utilize the emission from the excited singlet and triplet states, so these OLEDs can achieve an internal quantum efficiency of 100%, in principle. More recently, a third mechanism, thermally activated delayed fluorescence (TADF), was discovered, and practical materials are actively being developed.The final section of this chapter discusses the total light emission efficiency, which is very important in actual OLED devices.