Orientation of α-Sexithiophene on Friction-Transferred Polythiophene Film

Abstract

Controlling the molecular orientation of the conjugated oligomer, α-sexithiophene (6T), is crucial to improve organic optoelectronic device performance. Most 6T molecules evaporated onto quartz and SiO(2)/Si substrates orient nearly perpendicular to the substrate. Here, we report the formation of oriented thin films of 6T on in-plane-oriented polythiophene (PT) films formed by the friction-transfer method. 6T was evaporated onto oriented PT films under vacuum. The films were investigated by polarized optical microscopy, polarized ultraviolet-visible light (UV-vis) absorption spectroscopy, and grazing incidence X-ray diffraction measurement (GIXD). In all spectra, larger absorbance derived from PT and 6T was observed, in parallel polarization to the friction direction, compared to that of orthogonal polarization. These results indicate that the 6T molecular axis is aligned in the friction direction (PT chain direction) of PT films. GIXD also confirmed that the 6T molecular axis was aligned parallel to the PT chain axis. In contrast, 6T molecules evaporated onto quartz and poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-coated silicon substrates aligned nearly perpendicular to the substrate. These results indicate that oriented PT films induce 6T orientation parallel to the PT chain direction.

Solventless processing of conjugated polymers—A review

“…This molecular anisotropy and consequently anisotropic electron mobility can be used advantageously in circuit design, for example, to isolate neighboring components without requiring a large spatial separation or the patterning of the semiconductor layer [34]. In addition, in organic photovoltaic devices, where bias voltage is applied between top and bottom electrodes, it is expected that the increase in mobility due to crystal alignment in the direction perpendicular to the substrate will lead to improved power conversion efficiencies [35]. An example of this effect has been demonstrated in the use of a porous alumina template to prepare vertically aligned core-shell nanorods of P3HT and PCBM from the melt [22].…”

“…Mizokuru et al [35] reported the formation of oriented thin films of the oligothiophene ␣-sexithiophene (6T) deposited on to in-plane-oriented polythiophene (PT) films formed by friction-transfer. Thin films of 6T were evaporated onto an oriented 5 nm thick PT film, itself friction transferred at 250 • C, under vacuum.…”

Oriented Thin Films of Insoluble Polythiophene Prepared by the Friction Transfer Technique

“…We have already reported usages of friction-transferred PT films as orienting substrates for other semiconducting molecules [ 35 , 36 , 37 , 38 ]…”

Quasi-one-dimensional cyano-phenylene aggregates: Uniform molecule alignment contrasts varying electrostatic surface potential

“…31 Anisotropic substrates such as TiO 2 (11 0) 32,33 and Cu(11 0), 34,35 friction transferred poly-(tetrafluoroethylene) a) Author to whom correspondence should be addressed. Electronic mail: fbalzer@mci.sdu.dk (PTFE) and polythiophene, 36,37 and nanoporous substrates [38][39][40] have been used in the past as templates to form uniaxially aligned entities from organic molecules. Here, muscovite mica is used as a model substrate.…”