Efficient Electroluminescence from a Rubrene Sub-Monolayer Inserted between Electron- and Hole-Transport Layers

Efficient electroluminescence (EL) was obtained from rubrene by inserting its sub-monolayer between the Al-hydroxyquinoline (ALQ) and diamine layers. The highest EL current efficiency of 5.8 cd A-1 was attained by inserting a 0.05-nm-thick rubrene layer between the ALQ and diamine layers; in addition, the current-voltage curve was shifted to a lower voltage. These properties are favorable for the construction of efficient EL devices. The enhanced EL efficiency and the shift of the current-voltage curves are attributed to efficient trapping of holes by rubrene molecules at the interface.