A pyrimidine end-capped electron transport material interacted with silver for improving electron-injection and long-term stability in OLEDs†

Abstract

Although organic light-emitting devices (OLEDs) have been commercialized for display applications, electron-injection layers (EILs) still rely on alkali metals or their compounds to lower driving voltages, and hence reactivity with atmospheric moisture is a primary concern, especially in flexible devices. As an alternative strategy, combining electron transport materials (ETMs) based on 1,10-phenanthroline (Phen) derivatives with silver (Phen/Ag) has attracted much attention for developing air-stable EILs. However, most studies have focused on Phen derivatives. Herein, we developed a non-Phen ETM named DPmPy-BP based on a 2,6-di(pyrimidin-2-yl)pyridine skeleton. Combined with Ag (DPmPy-BP/Ag) as a potentially air-stable EIL, this ETM exhibited superior electron-injection properties and remarkable stability in preliminary green phosphorescent OLEDs achieving a maximum external quantum efficiency (EQE) of 20% and an operational lifetime (LT₅₀) of approximately 17 000 hours at 1000 cd m⁻², which surpass those of Phen/Ag devices and are comparable to devices using a conventional alkali metal compound 8-hydroxyquinolinolato-lithium (Liq) as the EIL (DPmPy-BP/Liq).