The influence of mechanical rubbing on the field-effect mobility in polyhexylthiophene

Abstract

Fabrication and characterization of solution-processed methanofullerene-based organic field-effect transistors J. Appl. Phys. 97, 083714 (2005); 10.1063/1.1895466Pentacene organic field-effect transistor on metal substrate with spin-coated smoothing layer This paper reports on improvements of the field-effect mobility in regioregular head-to-tail coupled poly͑3-hexylthiophene͒ based transistors by mechanically induced alignment of polymer chains in the active layer. It is demonstrated that mechanical rubbing perpendicular to the source drain contacts can increase the field-effect mobility up to 800% whereas rubbing parallel to the source drain contacts results in a reduced mobility. The polymer alignment is thereby deduced from optically polarized transmission spectroscopy on polymer-coated quartz glass substrates and is shown to directly correlate with the electrical behavior of a bottom-gate field-effect transistor. The influence of layer thickness on rubbing is investigated and it is shown that annealing after mechanical rubbing at high temperature can further increase the alignment. Differences between thick drop-cast and thin spin-coated films are explained in terms of different solvent evaporation rates, allowing the material to order to a different degree. This interpretation is deduced from characteristic optical and electrical features of the differently prepared poly͑3-hexylthiophene͒ films.

Structure and morphology control in thin films of regioregular poly(3‐hexylthiophene)

“…Oriented P3HT films with dichroic ratio of 5.1 were prepared but surprisingly, the charge mobility was improved when rubbing in the direction perpendicular to the source and drain contacts. 77 Using the principle of the friction-transfer method developed by Smith and Wittmann to prepare oriented PTFE layers, 78 Nagamatsu et al fabricated highly oriented P3HT films with typical dichroic ratio 10-100 indicating a very high level of in-plane alignment of the polymer chains with the c-axis parallel to the direction of friction transfer. 54 GIXD indicated that the p-stacking direction (b-axis) was perpendicular to the substrate plane, that is, the conjugated backbone adopts a ''flat-on'' orientation.…”

Anisotropic Charge Transport in Spherulitic Poly(3‐hexylthiophene) Films

“…It is therefore extremely difficult to study the impact of structural anisotropy and grain boundaries on charge-transport mobility in simple spin-cast films using macroscopic probes such as field-effect transistor (FET) channels since the device measurement necessarily averages over a very large number of randomly oriented boundaries. [9] One approach is to induce global orientation in the sample using mechanical rubbing, [13][14][15] imprinting, [16][17][18] alignment layers, [19] or directional solidification. [8,20] However, these methods introduce additional complications such as anisotropy in surface roughness (scratching) whose influence on the measured charge mobility (μ FET ) competes with and can obscure the effect of molecular orientation.…”

Some Air-stable Unsymmetrical Nickel 1,2-Dithiolenes with Extended Tetrathiafulvalenedithiolato Ligands

“…Some changes in the shape and intensity of the spectra after rubbing appear to be due to the partial orientation of molecules (see ref. [25] Fig. 1.…”