Annealing Solution-Processed CuSCN Hole Injection Layer for Blue Phosphorescent Organic Light-Emitting Diodes with Extremely Low Efficiency Roll-Off

Phosphorescent organic light-emitting diodes (PhOLEDs) have attracted tremendous attention recently but still suffer serious efficiency roll-off at high luminance, which will significantly limit their practical application in the future. Here, using a spin-coated transparent CuSCN film as the hole-injection layer (HIL), we succeed in achieving high-performance blue PhOLEDs with extremely low efficiency roll-offs based on widely used host and guest materials in a conventional device structure; by thermal and current annealing treatments, the external quantum efficiency (EQE) is up to 12.5% at 8370 cd m^-2, and the EQE roll-off can be as low as 2% at 10 000 cd m^-2 and 7% at 20 000 cd m^-2, respectively. The inorganic molecular semiconductor feature of CuSCN and the improved hole mobility after the annealing treatment were proved to be the main reasons for the highly stable PhOLEDs. The successful application of solution-processed CuSCN HIL for blue PhOLEDs with low efficiency roll-offs could provide important guidelines for the development of low-cost and highly efficient devices at high luminance.