Novel P-I-N-P top-emitting organic light-emitting diodes with enhanced efficiency and stability
An additional p-doping layer is added to the P-I-N stack of top-emitting organic light-emitting diodes (TEOLEDs) to control the electron tunneling current and improve interfacial stability. In addition, double p-doped layers, which are adjacent to the bottom-anode, are introduced to simultaneously optimize robustness and doping efficiency of p-type doping. In the emissive layer (EML), a second assistant emitter molecule is used which transfer its triplet energy to the actual emitter which is lower in energy, thus increasing the luminous efficacy. Such a co-doped dual-emitter layer is able to separate polarons and excitons and thus reduces chemical degradation. Compared to conventional P-I-N TEOLEDs, our novel P-I-N-P device shows negligible increase of driving voltage at low bias but offers significantly increased efficiencies. In addition, the P-I-N-P stack renders the electrical properties less sensitive to thickness variations and prolonged operation, which is attrib uted to the existence of a one-sided abrupt N-P tunneling junction beneath the top cathode contact.