Depletion- and ambipolar-mode field-effect transistors based on the organic heterojunction composed of pentacene and hexadecafluorophtholocyaninatocopper

We investigated heterojunction organic field-effect transistors (OFETs) using pentacene and hexadecafluorophtholocyaninatocopper (F₁₆CuPc) as double active layers. Two operation modes including depletion- and ambipolar-type were observed depending on the deposition order of two organic films. Depletion-mode was firstly observed from that devices with pentacene as the bottom layer and F₁₆CuPc as the top layer, which was attributed to dipole effects originated from the pentacene/F₁₆CuPc interface. Then improved device performances were obtained with mobility from 0.87 to 1.06 cm²/V s, and threshold voltage shifted from ?20 to +25 V as compared with conventional pentacene-based devices. Furthermore, the heterojunction OFETs exhibited typical ambipolar transport when alternating the deposition order of two films, which exhibited ambipolar mobilities with 0.06 cm²/V s for electron and 0.0025 cm²/V s for hole, respectively. All results implied the utilization of heterojunction can effectively improve the device performances of OFET, and operation mode strongly on the deposition order of two films.