Unveiling a pyridine-based exciplex host for efficient stable blue phosphorescent organic light-emitting diodes

Abstract

High triplet (T1) energy exciplex hosts show great potential for accelerating high efficiency and a prolonged lifetime for stable blue phosphorescent organic light-emitting diodes (PhOLEDs). However, achieving high efficiency and device stability simultaneously in PhOLEDs is hard-fought due to the lack of a stable host with high triplet energy and better charge balance ability. To address this issue, herein, we developed two electron transport (ET) n-type host materials, namely 9-(4-(6-cyanodibenzo[b,d]furan-2-yl)pyridin-2-yl)-9H-carbazole-3-carbonitrile (CNCzPyDFCN) and 9-(2-(8-cyanodibenzo[b,d]furan-2-yl)pyridin-4-yl)-9H-carbazole-3-carbonitrile (CNDFPyCzCN). The molecules were designed via quantum chemical/molecular dynamics (QC/MD) simulation methods. As a result, both ET n-type hosts achieved a high T1 of >2.96 eV and appropriate HOMO/LUMO energy level for outstanding electron-transporting properties. Furthermore, it was clarified that an exciplex was formed between our n-type hosts and p-type host 2,2′-di(9H-carbazol-9-yl)-1,1′-biphenyl (oCBP). Consequently, PhOLEDs were fabricated by introducing both exciplex systems and a blue phosphorescent emitter (CN–Ir). In particular, the device using oCBP:CNCzPyDFCN shows a high external quantum efficiency (EQE) of over 29% and a device lifetime of LT₅₀ 33.9 h at an initial luminescence of 1000 cd m⁻² with a low turn-on voltage. Thus, exciplex study with a high T1 host is a promising technology for long-term stable blue PhOLEDs.