Interfacial charges and electroluminescence in bilayer organic light-emitting diodes with different hole transport materials

Abstract

The performance of organic light-emitting diodes (OLEDs) and their interfacial charge density have been studied in tris-(8-hydroxyquinolate) aluminum (Alq3)-based OLEDs with four different hole transport layers (HTLs). The four HTLs have almost identical highest occupied molecular orbital (HOMO) energy levels. The performance of the four OLEDs is not greatly changed. The interfacial charge density is determined from the hole injection voltage in the capacitance - voltage characteristics of the OLEDs. Determination of the interfacial charge density is verified by device simulation. The interfacial charge density is dependent on the HTL materials in Alq3-based OLEDs, and is proportional to the difference in dipole moments between the HTLs and electron transport layers including Alq3