Enhanced Efficiency and Delayed Decay of Organic Light-Emitting Diodes by Incorporating Spacer Layer Based on Low-Triplet Energy Interfacial Exciplex

Although the performance of solution-processed organic light-emitting diodes (OLEDs) has been significantly increased, blue emission remains the key problem in the technology. Since the matched host materials should possess appropriate energy levels and high carrier mobility as well as higher triplet energies, it is really difficult to design and select the matched exciplex host materials. Herein, a simple donor–spacer–acceptor (D–S–A) structure for blue phosphorescent OLEDs with FIr6 as the blue emitter is reported. This design strategy is particularly efficient, and the performances of solution-processed blue phosphorescent OLEDs with a low triplet energy interfacial exciplex as the host were successfully enhanced by manipulating excitons and carriers via incorporating a bipolar spacer layer. The optimal device realized the maximum current efficiency of 31.99 cd/A, maximum external quantum efficiency of 19.01%, and maximum brightness of 15190 cd/m². The efficiency roll-off ratio at 1000 cd/m² was significantly decreased from 45.49% (primary device) to 10.00% (optimal device) due to improved carrier balance and well confined excitons. Notably, performances of the obtained device were better than the best records of solution-processed OLEDs with FIr6 as the emitter. More excitingly, this strategy is also successful in the development of high-performance white OLEDs.