Fullerene and Pentacene as a Pure Organic Connecting Layer in Tandem Organic Light Emitting Devices

A nondoped organic system of fullerene (C60)/pentacene was investigated as a connecting unit for green electroluminescent tandem organic light emitting devices with two identical emissive units consisting of ( -di(naphthalene-1-yl)- -diphthalbenzidine)/tris(8-hydroxyquinoline aluminum) ( ) that exhibited better current efficiency and current density characteristics over conventional devices. At , the current efficiency of the tandem devices using a nondoped organic layer of C60/pentacene was about 3.4 cd/A, almost 34% improvement over that of the corresponding conventional devices. The connecting unit showed a superior optical transparency, resulting in a minimal microcavity effect in the devices. Interface dipole and band bending on both sides of the C60/pentacene interface was suggested for the formation of an intrinsic p–n junction, which is a prerequisite of a connecting unit, leading to a significant performance improvement in the tandem devices.