Abstract
The correlation between molecular orientation and optoelectrical properties is most critical to the future design of molecular materials. We made highly-anisotropic microcrystalline array structures with an organic semiconductor, a methoxy-substituted thiophene/phenylene co-oligomer (TPCO), by depositing it on friction-transferred poly(tetrafluoroethylene) (PTFE) layers fabricated on substrates with several heat treatments. Polarising microscope observation, polarised emission and absorption spectra measurements indicated that the TPCO molecules aligned along the drawing direction of PTFE. Using these films, we fabricated two types of field-effect transistors (FETs) and compared them with those using non-heated TPCO films which provide aligned pleats structures. Ones had the channel length direction parallel to the drawing direction of PTFE and the others had the channel length direction perpendicular to that drawing direction. As for the microcrystalline array films, the mobility ratio of the former FET to that of the latter device was about 27 in the saturation region, while the emission polarisation ratio was 4.5. The heat treatment promoted the crystal growth to enhance the mobility while retaining the high anisotropy. The results demonstrate that the heat treatments of the TPCO films on the friction-transferred layers were useful for controlling crystallinity and orientation of the molecules.
Highlights
Organic materials are expected to be applied to unique devices including electronic papers and flexible displays by virtue of useful characteristics e.g. light-weight, flexible and printable
We have fabricated highly-anisotropic microcrystalline array structures by applying heat treatment to orientation films of a methoxy-substituted thiophene/phenylene co-oligomer (TPCO) deposited on friction-transferred PTFE layers to enhance the crystallinity and carrier mobility while retaining the high anisotropy
We prepared the organic field-effect transistors (OFETs) with orientation films on the PTFE layers with or without heat treatment during TPCO deposition
Summary
Organic materials are expected to be applied to unique devices including electronic papers and flexible displays by virtue of useful characteristics e.g. light-weight, flexible and printable. In applying the organic materials to devices, electronic and optical properties are affected by the characteristics of these materials and structural anisotropy and spatial overlap of the molecules such as crystallinity and orientation[1]. We made highly oriented films of thiophene/phenylene co-oligomers (TPCOs) by depositing them on friction-transferred PTFE layers fabricated on substrates[12] Even though these TPCO films indicated the anisotropic optical and electronic properties[12], it is desired to enhance the crystallinity as well. We have fabricated highly-anisotropic microcrystalline array structures by applying heat treatment to orientation films of a methoxy-substituted TPCO deposited on friction-transferred PTFE layers to enhance the crystallinity and carrier mobility while retaining the high anisotropy. We prepared the OFETs with orientation films on the PTFE layers with or without heat treatment during TPCO deposition
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