Abstract
Highly efficient yellow organic light-emitting diodes (OLEDs) with a solution-process feasible emissive layer were fabricated by simply using molecular hosts doped with an iridium-complex based yellow emitter. The best yellow OLED device studied here showed, at 100 cd/m2 for example, a power efficiency of 32 lm/W, a 113% improvement as comparing with the prior record, 15 lm/W, by using a polymeric host. The marked efficiency improvement may be attributed to the device that composed an electron-injection-barrier free architecture, the device structure that led the excitons to generate preferably on host to enable the efficiency-effective host-to-guest energy transfer to occur, and the employed molecular host that exhibited a good host-to-guest energy transfer. The efficiency was further improved to 53, 39 and 14 lm/W at 100, 1,000 and 10,000 cd/m2, respectively, with the use of a micro-lens. This study demonstrates also the possibility of achieving relatively high device efficiency for wet-processed OLED devices via balancing the injection of carriers, though based on commercially available OLED materials and limited design alternatives in device structure.