Precise Exciton Allocation for Highly Efficient White Organic Light‐Emitting Diodes with Low Efficiency Roll‐Off Based on Blue Thermally Activated Delayed Fluorescent Exciplex Emission

Abstract White organic light‐emitting diodes (WOLEDs) are highly attractive in the fields of solid‐state lighting. The biggest challenge that is facing at present is how to maximize the exciton utilization to further enhance the efficiency, while taking into account the stability. Here, highly efficient all‐fluorescence and fluorescence/phosphorescence (F/P) hybrid WOLEDs with low efficiency roll‐off by designing exciplex‐sandwich emissive architecture and precisely manipulating the exciton allocation are demonstrated. The resulting complementary‐color hybrid WOLEDs realize the maximum external quantum efficiency of 28.3% and power efficiency of 102.9 lm W⁻¹, and remain 26.9% and 73.5 lm W⁻¹ at 500 cd m⁻² and yet as high as 25.8% and 63.5 lm W⁻¹ at 1000 cd m⁻², respectively, revealing very low roll‐off. By using the efficient blue exciplex combined with red and green phosphorescent emitters, the three‐color WOLEDs yield a high color rendering index of 86, an external quantum efficiency of 29.4%, and a power efficiency of 75.5 lm W⁻¹. It is anticipated that the exciplex engineering will open an efficient avenue to precisely allocate excitons, and finally producing high‐performance WOLEDs for next‐generation solid‐state lighting technology.