Polymer-Based Organic Field-Effect Transistors with Active Layers Aligned by Highly Hydrophobic Nanogrooved Surfaces

In this study, polymer-based organic field-effect transistors (OFETs) that exhibit alignment-induced mobility enhancement, very small device-to-device variation, and high operational stability are successfully fabricated by a simple coating method of semiconductor solutions on highly hydrophobic nanogrooved surfaces. The highly hydrophobic nanogrooved surfaces (water contact angle >110 degrees) are effective at inducing unidirectional alignment of polymer backbone structures with edge-on orientation and are advantageous for realizing high operational stability because of their water-repellent nature. The dewetting of the semiconductor solution is a critical problem in the thin film formation on highly hydrophobic surfaces. Dewetting during spin coating is suppressed by surrounding the hydrophobic regions with hydrophilic ones under appropriate designs. For the OFET array with an aligned terrace-phase active layer of poly(2,5-bis(3-hexadecylthiophene-2-yl)thieno[3,2-b]thiophene), the hole mobility in the saturation regime of 30 OFETs with channel current direction parallel to the nanogrooves is 0.513 +/- 0.018 cm(2) V-1 s(-1), which is approximately double that of the OFETs without nanogrooves, and the intrinsic operational stability is comparable to the operational stability of amorphous-silicon field-effect transistors. In other words, alignment-induced mobility enhancement and high operational stability are successfully achieved with very small device-to-device variation. This coating method should be a promising means of fabricating high-performance OFETs.