Interface Exciplex Anchoring the Color Stability of Solution‐Processed Thermally Activated Delayed Fluorescent White Organic Light‐Emitting Diodes

Abstract Spectral stability and high color rendering index (CRI) remain challenges to high‐performance, solution‐processed white organic light‐emitting devices (WOLEDs) based on two complementary colors. The solution‐processed WOLED based on two thermally activated delayed fluorescence emitters with complementary color, i.e., the orange–red 2‐[4‐(diphenylamino) phenyl]‐10,10‐dioxide‐9H‐thioxanthen‐9‐one emitter and the blue 4,4′‐bis(carbazol‐9‐yl)‐2,2′‐dimethylbiphenyl:4,6‐bis(3,5‐di(pyridin‐4‐yl)phenyl)‐2‐phenylpyrimidine interface exciplex, is reported here. Poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐(4,4′‐(N‐(4‐sec‐butylphenyl)) diphenylamine)] is doped with 30 wt% cross‐linkable N,N′‐(4,4′‐(cyclohexane‐1,1‐diyl)bis(4,1‐phenylene))bis(N‐(4‐(6‐(2‐ethyloxetan‐2‐yloxy)hexyl)phenyl)‐3,4,5‐trifluoroaniline) to form a smooth hole transportation layer with outstanding solvent resistance ability and efficient hole transporting/injection ability. The position of interface exciplex and exciton management in the emitting layer can be tuned, thus anchoring the color stability. The device displays a maximum external quantum efficiency of 10.02% and a high CRI of 85 with Commission Internationale de l'Eclairage (CIE) color coordinates of (0.32, 0.33) at the luminescence of 1000 cd m⁻². These results are among the best of solution‐processed WOLEDs based on two complementary chromophores.