Abstract
Deep-red emission can be applied for fabricating high quality, wide color gamut displays as well as physiologically-friendly, low color temperature lighting source. Emitters with wet-process feasibility are highly desirable to fabricate cost-effective large-area-size devices via roll-to-roll fabrication. We demonstrate here the high-efficiency, wet-process feasible deep-red organic light-emitting diodes by using a suitable co-host structure coupling with a phosphorescent emitter, [bis-(spirofluorene-dibenzosuberene[d]quinoxaline-C2,N)-monoacetylacetona-te]iridium(III), using doubly ortho-linked qiunoxaline/diphenylfluorene hybrids as ligands. The resulting device shows an external quantum efficiency (EQE) of 8.4% with CIExy (0.70, 0.27) at 100 cd/m2 and a maximum EQE of 11.2% with CIExy (0.72, 0.27) at 10 cd/m2, the highest EQE among all reported deep-red devices via wet-process. From material perspective, the record high efficiency may be attributed to the spirally configured fluorene moiety to prevent concentration-quenching effect and the high molecular weight of the emitter to enable the wet-processed emissive layer with good film-forming property. From device architecture perspective, the high efficiency may be attributed to a paired host and guest energy-levels to allow excitons generated on the host, a proper host to enable an effective host-to-guest energy transfer, and the employed host/co-host with electron trapping character to enable a balanced carrier injection.