title: pn-Heterojunction effects of perylene tetracarboxylic diimide derivatives on pentacene field-effect transistor.
abstract: We investigated the heterojunction effects of perylene tetracarboxylic diimide (PTCDI) derivatives on the pentacene-based field-effect transistors (FETs). Three PTCDI derivatives with different substituents were deposited onto pentacene layers and served as charge transfer dopants. The deposited PTCDI layer, which had a nominal thickness of a few layers, formed discontinuous patches on the pentacene layers and dramatically enhanced the hole mobility in the pentacene FET. Among the three PTCDI molecules tested, the octyl-substituted PTCDI, PTCDI-C8, provided the most efficient hole-doping characteristics (p-type) relative to the fluorophenyl-substituted PTCDIs, 4-FPEPTC and 2,4-FPEPTC. The organic heterojunction and doping characteristics were systematically investigated using atomic force microscopy, 2D grazing incidence X-ray diffraction studies, and ultraviolet photoelectron spectroscopy. PTCDI-C8, bearing octyl substituents, grew laterally on the pentacene layer (2D growth), whereas 2,4-FPEPTC, with fluorophenyl substituents, underwent 3D growth. The different growth modes resulted in different contact areas and relative orientations between the pentacene and PTCDI molecules, which significantly affected the doping efficiency of the deposited adlayer. The differences between the growth modes and the thin-film microstructures in the different PTCDI patches were attributed to a mismatch between the surface energies of the patches and the underlying pentacene layer. The film-morphology-dependent doping effects observed here offer practical guidelines for achieving more effective charge transfer doping in thin-film transistors.
authors.affiliation: Department of Chemical Engineering and ‡SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University , Suwon, 440-746, Korea.
authors.forename: Seong Hun
authors.initials: SH
authors.lastname: Yu
authors.forename: Boseok
authors.initials: B
authors.lastname: Kang
authors.forename: Gukil
authors.initials: G
authors.lastname: An
authors.forename: BongSoo
authors.initials: B
authors.lastname: Kim
authors.forename: Moo Hyung
authors.initials: MH
authors.lastname: Lee
authors.forename: Moon Sung
authors.initials: MS
authors.lastname: Kang
authors.forename: Hyunjung
authors.initials: H
authors.lastname: Kim
authors.forename: Jung Heon
authors.initials: JH
authors.lastname: Lee
authors.forename: Shichoon
authors.initials: S
authors.lastname: Lee
authors.forename: Kilwon
authors.initials: K
authors.lastname: Cho
authors.forename: Jun Young
authors.initials: JY
authors.lastname: Lee
authors.forename: Jeong Ho
authors.initials: JH
authors.lastname: Cho
keywords: charge transfer doping; organic field-effect transistor; pentacene; perylene tetracarboxylic diimide; pn-heterojunction