High-Performance Exciplex-Type Host for Multicolor Phosphorescent Organic Light-Emitting Diodes with Low Turn-On Voltages

Abstract

Rational design and selection of suitable donor and acceptor components for optimal thermally activated delayed fluorescence (TADF) exciplex-type emitters or hosts is presently challenging. Here, we constructed successfully a blue-emitting bulk exciplex system with efficient TADF emission and high triplet energy (ET) based on a donor of 4,4′,4′′-tris [3-methylphenyl(phenyl)amino]triphenylamine and an acceptor of 1,3,5-tri (m-pyrid-3-yl-phenyl)benzene. Systematic experimental and theoretical studies show that the matched frontier orbital energy levels, high ET, facile intersystem crossing, high oscillator strength of the exciplex, and efficient energy transfer channels should be the main considerations during the design of high-performance exciplex-type TADF emitters and bipolar host materials. Therefore, this bulk exciplex system can behave not only as blue emitters for organic light-emitting diodes (OLEDs) but also as universal hosts for the green, yellow, and red phosphorescent OLEDs (PhOLEDs). Impressively, even under a very low guest doping level of 2 wt %, the PhOLEDs exhibit very low turn-on voltages (∼2.2 V) and high maximum external quantum efficiencies up to 18.5%. These promising device results, along with the theoretical understandings, could shed important light on the rational design of exciplex systems and their applications as either TADF emitters or bipolar host materials for high-performance and low-cost OLEDs.