White OLEDs with an EQE of 21% at 5000 cd m −2 and Ultra High Color Stability Based on Exciplex Host

Exciplex has drawn attention because of its great potential for use as a host in organic light‐emitting diodes (OLEDs). Here a novel exciplex host formed with 3,3′‐di(9 H ‐carbazol‐9‐yl) biphenyl (m‐CBP) and 4,6‐bis (3,5‐di(pyridin‐4‐yl) phenyl)‐2‐phenylpyrimidine (B4PyPPM) is achieved. By utilizing m‐CBP:B4PyPPM exciplex host, blue, cyan, green, and red phosphorescent OLEDs exhibit maximum external quantum efficiencies (EQEs) of 26.2%, 26.1%, 24.7%, and 26.5%, respectively. Moreover, single‐emitting layer (EML) white organic light‐emitting devices (WOLEDs) are achieved by doping blue and red phosphorescent emitters, which exhibit high maximum EQEs of 23.9% and 26.9%. Even at a practical brightness of 5000 cd m −2 , the two WOLEDs still keep high EQEs of 19.1% and 21.0%, respectively. Furthermore, multiple‐EML WOLEDs are also constructed with efficiencies of 18.9% and 21.0% at the practical brightness of 5000 cd m −2 . The devices show extremely stable white emission with small Commission Internationale de L'Eclairage (CIE) coordinate varying range of (±0.001, ± 0.000) from 100 to 100 00 cd m −2 . The outstanding features presented here can provide a good reference for future design of high‐performance WOLEDs.