High-Performance, Phosphorescent, Top-Emitting Organic Light-Emitting Diodes with p-i-n Homojunctions

High-performance, green, orange, and red top-emitting organic light-emitting diodes (TOLEDs) with p-i-n homojunction are demonstrated. An excellent ambipolar host, 2,5-bis(2-(9H-carbazol-9-yl) phenyl)-1,3,4-oxadiazole (o -CzOXD), which has good thermal and morphological stabilities, a high triplet energy level, and equally high electron and hole mobilities, is chosen as the organic host material for the homojunction devices. By electrical doping, the carrier injection and transporting characteristics are greatly improved. The optical structure is optimized in view of light emission of different colors to enhance the color purity and improve the view characteristics. As a result, high efficiency p-i-n homojunction TOLEDs with saturated intrinsic emission of the emitting materials and angular independence of the emission are realized. The performances of these p-i-n homojunction TOLEDs are even higher than the multi-layer heterojunction bottom-emitting devices using the same emitting layers.