Enhancement of efficiency and stability of phosphorescent OLEDs based on heterostructured light-emitting layers

摘要

The light-emitting efficiency and stability of a phosphorescent organic light-emitting device (OLED), whose emission characteristics are strongly dominated not only by the energy transfer but also by the charge carrier trapping influenced by heterostructured emissive layers, are studied. The variation of the material combination of the heterostructured emitter, both for mixed and double layer configuration, affects the charge injection behaviour, luminous efficiency and stability. Both double and mixed emitter configurations yield low-voltage and high-efficiency behaviour (51 lm W~(-1) at 1000 cd m~(-2); 30 lm W~(-1) at 10 000 cd m~(-2)). Such an improvement in power efficiency at elevated brightness is sufficiently universal, while the enhancement of device half-lifetime is rather sensitive to the circumstantial layout of heterostructural emitters. With an optimal mixture of hole-transport type and electron-transport type, a half-lifetime of more than 2500 h at 4000 cd m~(-2) is obtained, which is 8 times the half-lifetime of control devices with a single emitter structure. The origin and criterion for enhancement of efficiency and lifetime are discussed in terms of the carrier transport behaviour with a specific device architecture.