Despite tremendous progress made in the synthesis of surface-grafted polymer brushes, there have been few reports of polymer brushes in organic electronics. Polymer brushes are promising for organic electronics because they exhibit a higher degree of ordering and better uniformity than spin-cast films. In the conventional “grafting-from” method, the synthesis of conjugated polymers with controlled structure and composition usually requires reaction conditions and techniques that cannot be easily employed on inorganic surfaces. We report a versatile “grafting-to” approach based on click chemistry to prepare poly(3-hexylthiophene) (P3HT) brushes on oxide substrates. P3HT is an important polymeric semiconductors in electronic applications such as field-effect transistors and photovoltaics. Regioregular ethynyl-terminated P3HT with molecular weight of 5900 g/mol and polydispersity of 1.2 was synthesized by catalyst-transfer polycondensation using Grignard metathesis mediated by a nickel-based catalyst. The azide monolayer was prepared from bifunctional molecules containing an azide click reaction precursor and a siloxane surface linker. The P3HT brushes were characterized by atomic force microscopy, ellipsometry, X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and UV-visible spectroscopy. The grafting of P3HT brushes was studied as a function of click reaction time and the growth of the brushes is governed by a diffusion-controlled process. P3HT brushes were prepared on the pre-fabricated field-effect transistor structures in order to probe the electrical properties of the brushes. The saturation hole mobility for P3HT brushes measured in an FET structure was 5 x 10-5 cm2/Vs, which is comparable to hole mobilities in FETs with monolayer-thick dip-coated P3HT. We have further shown the generalization of this chemistry to the wide-bandgap semiconductor ZnO, which is especially challenging as it requires mild conditions to prevent etching ZnO. The versatile synthetic methodology developed in this work can be generalized to prepare a wide variety of semiconducting conjugated polymer brushes on oxide surfaces relevant to organic electronic devices.

Figure Caption: Synthetic scheme for a) 3-azidopropyltrimethoxysilane (1). b) 2,5-dibromo-3-hexylthiophene (2) and ethynyl-terminated P3HT (3). c) anchoring of ethynyl-terminated P3HT(3) by click chemistry to a SAM of azide (1) .

Grafting of Conjugated Polymers on Oxide Surfaces

Figure Caption: a) Illustration of the bottom-contact FET device configuration with P3HT brushes, b) transistor characteristic curves of P3HT brushes measured at drain voltage of -20 V, c) UV-visible spectra of P3HT brushes on glass substrate, and d) thicknesses of P3HT brushes measured by ellipsometry as a function of reaction times.

c) d)

Paoprasert, P.; Spalenka, J. W.; Peterson, D. L.; Ruther, R. E.; Hamers, R. J.; Evans, P. G.; Gopalan, P, J. Mater. Chem. 2010. 20, 2651-2658.

UW MRSEC DMR-0520527Juan J. de Pablo, PI

University of Wisconsin-MadisonMaterials Research Science & Engineering Center on Nanostructured Interfaces

P. Paoprasert, J. Spalenka, D.L. Peterson, R. Ruther, R.J. Hamers, P.G. Evans, P. Gopalan