Controllably Tuning Excited-State Energy in Ternary Hosts for Ultralow-Voltage-Driven Blue Electrophosphorescence

摘要

Phosphorescent organic light-emitting diodes (PHOLEDs), with 100% theoretical internal efficiency, are being rapidly developed as a most promising approach to meet the urgent and extensive demand of energγ-efficient and portable digital terminals and lighting sources. Thanks to the recent breakthrough of highly efficient blue PHOLEDs and out-coupling technologies, PHOLEDs in full color can already realize extremely high efficiencies that approach those of fluorescent tubes (about 70 Lm W~(-1)). Nevertheless, as the hosts in the emitting layers (EMLs) should have higher triplet excited energy levels (T1) to confine the excitons on phosphorescent guests, the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps in PHOLEDs are often much larger than their fluorescent counterparts, which consequently result in poor energγ-level alignment and thus higher driving voltages. This drawback not only complicates the design of driving circuit, but also directly reduces power efficiency (PE). Thus, the low-voltage-driving high-efficiency PHOLED remains the biggest challenge.