The effect of copper hexadecafluorophthalocyanine (F16CuPc) inter-layer on pentacene thin-film transistors

We report the impact of a copper hexadecafluorophthalocyanine (F16CuPc) layer inserted between the electrode (Ag and Au) and the pentacene active layer in organic thin-film transistors (OTFTs). The electrical characteristics of the transistor are highly improved with the insertion of F16CuPc in devices having either an Ag or an Au electrode. The threshold voltage was reduced remarkably from −26.20 V to −3.72 V after inserting the F16CuPc layer in the device with an Ag electrode. In order to examine the effect of the F16CuPc layer, we evaluated the energy level alignments at the interfaces of pentacene/Ag and pentacene/F16CuPc/Ag by in situ ultraviolet photoelectron spectroscopy. The hole-injection barrier from the Ag electrode to the pentacene layer is 0.55 eV with F16CuPc, while it is 0.80 eV without F16CuPc. The enhancements in the threshold and turn-on voltages are understood with the energy level alignments at the electrode–pentacene interface.