Effect of flexibility on the formation of conducting layers at organic single crystal heterointerfaces

The electrical conductivities of organic single crystal heterointerfaces are investigated. Electron transfer at the rubrene/7,7,8,8- tetracyanoquinodimethane (TCNQ) interface from the highest occupied molecular orbital of rubrene to the lowest unoccupied molecular orbital of TCNQ imparts conductivity to the interface. A conducting layer is formed at a rubrene-on-TCNQ heterointerface, but not at a TCNQ-on-rubrene heterointerface fabricated on a rigid SiO2/Si substrate. The formation of an interfacial conducting layer requires a good contact between two single crystals; therefore, the experimental results might be explained by the poor adherence of rather thick TCNQ crystals to the rigid rubrene/SiO2/Si system.