Charge separation and transport behavior of a two-dimensional charge sheet at organic donor-acceptor heterointerfaces

Abstract

Charge separation and transport behavior were investigated at an organic heterolayered interface consisting of a 4,4′,4″-tris[3-methylphenyl(phenyl)amino] triphenylamine (m-MTDATA) organic donor and a hexadecafluoro-copper-phthalocyanine (F16CuPc) organic acceptor. A two-dimensional charge sheet of electron-hole pairs was induced due to the formation of charge-transfer complexes at the heterointerface. The induced charges could be separated by application of an electric field perpendicular to the heterointerface. The charge-separation behavior was independent of the work function of the contact electrodes but was strongly dependent on the energy-level alignment between the highest occupied molecular orbital of the donor molecules and the lowest unoccupied molecular orbital of the acceptor molecules. This enabled the preparation of an organic light-emitting diode without injecting holes from the anode. The charge-transport behavior along the heterointerface was also investigated by fabricating laterally arranged contact electrodes. The F16CuPc/m-MTDATA heterointerface exhibited high conductivity of 0.001 S/cm, which is seven orders of magnitude higher than that of a single-layer F16CuPc or m-MTDATA film. In situ electrical measurements during formation of the heterointerface enabled the effective thickness of the charge sheet to be determined as being accumulated within 2–3 nm, which corresponds to the bilayer of both F16CuPc and m-MTDATA.