Strategically Modulating Carriers and Excitons for Efficient and Stable Ultrapure‐Green Fluorescent OLEDs with a Sterically Hindered BODIPY Dopant

Abstract Ultrapure colors are vital for displays to obtain the highly desired wide color‐gamut. Till now, only boron‐dipyrromethene derivatives (BODIPYs) have demonstrated ultrapure full‐colors but suffer from low excitons utilization efficiency as dopants in organic light‐emitting diodes. It is proposed here that with a thermally activated delayed fluorophore to sensitize BODIPYs, all excitons can be recycled, which, still, is challenged by exciton loss through Dexter energy transfer (DET) from sensitizer to dopant and direct charge trapping on BODIPYs. Hence, a sterically hindered BODIPY‐type dopant with a bulk substituent on the meso‐position is developed to suppress DET, exhibiting a high photo‐luminance quantum yield of 98% and a small full width at half maximum of 28 nm. Moreover, the device structure is elaborately designed, successfully modulating carriers and excitons to avoid charge trapping on dopant and also trigger multiple‐sensitizing processes to reduce exciton loss. Consequently, a state‐of‐the‐art maximum external quantum efficiency/power efficiency of 19.0%/85.7 lm W −1 are realized together with an ultrapure‐green emission of Commission Internationale de l'Eclairage coordinates of (0.26, 0.67) and a long half‐lifetime of 2947 h at an initial luminance of 1000 cd m −2 .