Charge transfer effects in organic field-effect transistors containing a donor/acceptor heterojunction

Heterojunction organic field-effect transistors (OTFTs) based on copper phthalocyanine (CuPc) as p-type and on copper hexadecafluorophthalocyanine (F16CuPc) or 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as n-types were fabricated and studied. They were shown to operate in unipolar mode where hole current was recorded with values approaching those of CuPc-based single-layer device. However, due to a charge transfer phenomenon between CuPc and F16CuPc, the occurrence of a build-in electrical field at the CuPc/F16CuPc interface is shown to influence the transport properties at low drain-source voltages and to induce a non-ideal ohmic behavior in OTFT characteristics. This effect is not observed in the case of CuPc/TCNQ because of a larger energy difference between HOMO and LUMO energy levels of CuPc and TCNQ, respectively.