Host and Dopant Materials for Idealized Deep-Red Organic Electrophosphorescence Devices

摘要

The performance of organic light-emitting diodes (OLEDs) can be greatly improved by using phosphorescent materials because both the singlet and triplet excitons can be harvested and the internal quantum efficiency can reach as high as 100%.[1] To reduce the self-quenching and triplet-triplet (TT) annihilation and to achieve a high efficiency for phosphorescence organic light-emitting diodes (PhOLEDs), a proper combination of the host and dopant system is vital.'21 For full-color applications, a search for efficient host and dopant materials are generally required for all three primary colors (red, green, and blue).[3] The carbazole-based host material 4,4'-bis(9-carbazolyl)-2,2'- biphenyl (CBP)[1c,2a] has been widely used in red PhOLEDs. However, its relatively low glass transition temperature, T_g = 62 °C, results in poor morphological stability.[4] In addition, the large energy gap impedes charge carrier injection from adjacent carrier-transporting layers. Therefore, a large driving voltage is usually required for the CBP-based devices.[5]