Donor engineered Deep-Blue emitters for tuning luminescence mechanism in Solution-Processed OLEDs

Abstract

Three novel solution-processable A-π-2D-type deep-blue emitters, namely BCz, BBFCz, and BICz, were developed to investigate their luminescence mechanisms and performances in organic light-emitting diodes (OLEDs). The emitters were uniquely designed by connecting two carbazole analogs as donors and a boron-fused unit as an electron acceptor to the benzene core; they exhibited aggregation-induced emission properties in the film states. Theoretical calculations and time-resolved photoluminescence (TRPL) experimental results indicate that the luminescence mechanism of the three emitters changed from fluorescence to thermally activated delayed fluorescence (TADF) as the donor unit was changed from carbazole to indenocarbazole. BCz was found to act like a fluorescent emitter, but BBFCz and BICz displayed TADF characteristics. Efficient reverse intersystem crossing (RISC) in BICz was confirmed by small ΔEST, Ea, and kISC/kRISC ratio. Consequently, non-doped solution-processed TADF-OLEDs based on BICz as an emitter exhibited the highest external quantum efficiency (EQE) of 10.11%, with deep-blue commission International de ĺEclairage (CIE) color coordinates (0.16, 0.08). In contrast, BCz- and BBFCz-based devices showed relatively lower EQEs of 3.44% and 6.78%, respectively. The results showed that BICz as an emitter displayed exceptional performance in a non-doped solution-processed deep-blue TADF-OLED. © 2021