Enhanced Efficiency\nand Delayed Decay of Organic Light-Emitting\nDiodes by Incorporating Spacer Layer Based on Low-Triplet Energy Interfacial\nExciplex

Although the performance of solution-processed\norganic\nlight-emitting\ndiodes (OLEDs) has been significantly increased, blue emission remains\nthe key problem in the technology. Since the matched host materials\nshould possess appropriate energy levels and high carrier mobility\nas well as higher triplet energies, it is really difficult to design\nand select the matched exciplex host materials. Herein, a simple donor–spacer–acceptor\n(D–S–A) structure for blue phosphorescent OLEDs with\nFIr6 as the blue emitter is reported. This design strategy is particularly\nefficient, and the performances of solution-processed blue phosphorescent\nOLEDs with a low triplet energy interfacial exciplex as the host were\nsuccessfully enhanced by manipulating excitons and carriers via incorporating\na bipolar spacer layer. The optimal device realized the maximum current\nefficiency of 31.99 cd/A, maximum external quantum efficiency of 19.01%,\nand maximum brightness of 15190 cd/m<sup>2</sup>. The efficiency roll-off\nratio at 1000 cd/m<sup>2</sup> was significantly decreased from 45.49%\n(primary device) to 10.00% (optimal device) due to improved carrier\nbalance and well confined excitons. Notably, performances of the obtained\ndevice were better than the best records of solution-processed OLEDs\nwith FIr6 as the emitter. More excitingly, this strategy is also successful\nin the development of high-performance white OLEDs.