title: Engineering Thin Films of a Tetrabenzoporphyrin toward Efficient Charge-Carrier Transport: Selective Formation of a Brickwork Motif.
abstract: Tetrabenzoporphyrin (BP) is a p-type organic semiconductor characterized by the large, rigid π-framework, excellent stability, and good photoabsorption capability. These characteristics make BP and its derivatives prominent active-layer components in organic electronic and optoelectronic devices. However, the control of the solid-state arrangement of BP frameworks, especially in solution-processed thin films, has not been intensively explored, and charge-carrier mobilities observed in BP-based materials have stayed relatively low as compared to those in the best organic molecular semiconductors. This work concentrates on engineering the solid-state packing of a BP derivative, 5,15-bis(triisopropylsilyl)ethynyltetrabenzoporphyrin (TIPS-BP), toward achieving efficient charge-carrier transport in its solution-processed thin films. The effort leads to the selective formation of a brickwork packing that has two dimensionally extended π-staking. The maximum field-effect hole mobility in the resulting films reaches 1.1 cm2V-1s-1, which is approximately 14 times higher than the record value for pristine free-base BP (0.070 cm2V-1s-1). This achievement is enabled mainly through the optimization of three factors; namely, deposition process, cast solvent, and self-assembled monolayer that constitutes the dielectric surface. On the other hand, polarized-light microscopy and grazing-incident wide-angle X-ray diffraction analyses show that there remains some room for improvement in the in-plane homogeneity of molecular alignment, suggesting even higher charge-carrier mobilities can be obtained upon further optimization. These results will provide a useful basis for the polymorph engineering and morphology optimization in solution-processed organic molecular semiconductors.
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology , 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan.
authors.forename: Kohtaro
authors.identifier: http://orcid.org/0000-0001-7249-8985
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong, China.
authors.forename: Bowen
authors.initials: B
authors.lastname: Shan
authors.affiliation: Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong, China.
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Xu
authors.affiliation: Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong, China.
authors.forename: Shuaijun
authors.initials: S
authors.lastname: Yang
authors.affiliation: Japan Synchrotron Radiation Research Institute (JASRI) , SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Koganezawa
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology , 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan.
authors.forename: Daiki
authors.initials: D
authors.lastname: Kuzuhara
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology , 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Aratani
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology , 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan.
authors.forename: Mitsuharu
authors.identifier: http://orcid.org/0000-0002-0121-2561
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Miao
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology , 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yamada
keywords: brickwork packing; dip coating; organic thin-film transistors; polymorphism; self-assembled monolayers (SAMs); tetrabenzoporphyrin (BP)