Combining intrinsic (blue) and exciplex (green and orange-red) emissions of the same material (OCT) in white organic light-emitting diodes to realize high color quality with a CRI of 97

Abstract

A deep-blue material with excellent bipolar carrier transport ability, 2-(4-(3-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazol-9-yl)phenyl)benzo[d]oxazole (OCT), was reported in our previous work. In this work, employing OCT as an electron acceptor and matching it with different electron donors (TAPC and m-MTDATA), green and orange-red exciplex-based organic light-emitting diodes (OLEDs) have been demonstrated for the first time, with emission peaks located at 524 nm and 596 nm and broader full widths at half maximum reaching 102 nm and 117 nm, respectively, which are quite beneficial for developing high-color-quality white OLEDs. The green device also realized high electroluminescence performance, with its maximum current efficiency, power efficiency and external quantum efficiency reaching 34.6 cd A⁻¹, 40.2 lm W⁻¹, and 10.6%, respectively, which originated from efficient reverse intersystem crossing owing to the small energy gap between the singlet and triplet levels for the TAPC:OCT-forming exciplex. On the basis of the above considerations, adopting OCT as a blue emitter and exciplex acceptor, three-color white OLEDs were designed and fabricated by simultaneously combining the blue intrinsic emission with the green and orange-red exciplex emissions based on OCT. The optimized device realizes very good white emission, with a maximum color rendering index of 97, which, to the best of our knowledge, is among the highest CRIs reported for three-color white OLEDs. The achievement of such high color quality is closely related to the wide emission spectrum of OCT-based exciplexes. This is also the first reported three-color white device realized by simultaneously combining the intrinsic emission and complementary exciplex emissions of the same material, which may provide a new avenue for designing high-performance white OLEDs in the future.