Evolution of Red Organic Light-Emitting Diodes:  Materials and Devices

This short review surveys the development of red fluorescent materials for the application of organic light-emitting diodes (OLEDs) that generate red electroluminescence (EL). The merit and problems of current dopant-based, either fluorescent or phosphorescent, red OLEDs will be addressed first. Materials that offer unique EL characteristics, such as narrow and saturated red EL as well as current density or voltage-independent EL efficiency, are discussed. In addition to dopant-based and assist dopant-based red OLEDs for comparison purposes, the survey emphasizes nondoped red OLEDs that are fabricated with the newly emerging red fluorophores as the host-emitter. The advantage of host-emitting nondoped OLEDs compared with traditional dopant-based red OLEDs is described in view of the chemical and device structures of these materials.