Single-layer small molecular organic light emitting diodes without hole transport layer

Organic light emitting devices based on tris-8-hydroxyquinoline aluminum with an ultra-thin insulating film instead of a hole-transporting layer were investigated. Three kinds of single-layer devices were fabricated with silicon dioxide (SiO₂), alumina (Al₂O₃) or polytetrafluoroethylene (Teflon™) as the insulating films, and they showed better performance than devices without insulating films. The hole injection of these devices was also investigated using hole-only devices. The holes injection enhancement by tunneling effect and electrons blocking of the ultra-thin insulating layers were experimentally proved to have yielded high performance of single-layer devices.