Development of a deep-blue exciplex as an emitter and a host for highly efficient and wide-color OLEDs

Abstract

Exciplex emission with thermally activated delayed fluorescence (TADF) characteristics has been widely applied in organic light-emitting diodes (OLEDs). Owing to its intermolecular charge transfer feature, development of an exciplex with a wide bandgap for deep-blue OLEDs is still challenging. Herein we designed a deep-blue exciplex system consisting of 3,3′-di(9H-carbazol-9-yl) biphenyl (mCBP) and difluoroboron(Z)-3-(diphenylamino)-3-hydroxy-N,N-diphenylacrylamide (DNPhB) as the electron acceptor and the donor, respectively, which exhibit a deep-blue emission at 444 nm and a high photoluminescence quantum yield (PLQY) of 56%. The high triplet energy level enables the mCBP:DNPhB exciplex not only as a TADF emitter but also as a host with efficient Dexter energy transfer to a variety of phosphorescent molecules. A deep-blue OLED fabricated using the exciplex emitter shows the Commission Internationale de L'Eclairage (CIE) coordinates of (0.152, 0.075) as well as a high EQE of 4.83% and a high brightness up to 5486 cd m⁻². Moreover, wide-color phosphorescent OLEDs (PhOLEDs) were fabricated by using the exciplex as a host. The brightness of a green PhOLED based on the Ir(ppy)₃ emitter is up to 150 000 cd m⁻². This work paves the way to achieve a high-performance deep-blue exciplex OLED to meet the demand for potential applications such as a wide color display.