Triplet exciton energy manipulation toward low turn-on voltage and efficient fluorescent blue organic light-emitting diodes

Abstract

Fluorescent blue emitters, which are mostly limited to the utilization of singlet excitons, remain the predominant choice in commercial organic light-emitting diodes (OLEDs) owing to the undesirable operational stability of their phosphorescent counterparts. However, the compromised device efficiency and high turn-on voltage (Von) hinder their development. Here, we report an effective interfacial charge-transfer manipulation strategy for realizing efficient blue fluorescent OLEDs. By tailoring the material compositions of the electron transport layer (ETL) to form exciplex excitons at the emitting layer/ETL interface, the energy required for exciton formation can be effectively reduced, which enables increased exciton density at low operating voltages. Furthermore, by employing the anthracene-based material 2-[4–(9,10-Di-2-naphthalenyl-2-anthracenyl)phenyl]-1-phenyl-1H-benziMidazole (ZADN) as the host to promote triplet–triplet upconversion within the EML, low-energy triplet excitons in fluorescent blue OLEDs can be utilized. As a result, the optimized blue fluorescent device, with ZADN as the host material and 4,6-Bis(3,5-di(pyridin-4-yl) phenyl)-2-Methylpyrimidine as the ETL, illustrates a low Von of 2.2 V, a maximum brightness of 53 200 cd/m2, and a high external quantum efficiency (EQE) of 5.1%. Based on this strategy, white-color tandem OLEDs with an EQE of 12% and brightness of 650 cd/m2 at 5 V are achieved.