Doping of Conjugated Polythiophenes with Alkyl Silanes

• Published in: Advanced functional materials Vol. 19; no. 12; pp. 1906 - 1911
• Main Authors: Kao, Chi Yueh, Lee, Bumsu, Wielunski, Leszek S., Heeney, Martin, McCulloch, Iain, Garfunkel, Eric, Feldman, Leonard C., Podzorov, Vitaly
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 23.06.2009; WILEY‐VCH Verlag
• Subjects: charge transport; conjugated polymers; doping; polythiophenes; self-assembled monolayers
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200900120

A strong modification of the electronic properties of solution‐processable conjugated polythiophenes by self‐assembled silane molecules is reported. Upon bulk doping with hydrolized fluoroalkyl trichlorosilane, the electrical conductivity of ultrathin polythiophene films increases by up to six orders of magnitude, reaching record values for polythiophenes: (1.1 ± 0.1) × 103 S cm−1 for poly(2,5‐bis(3‐tetradecylthiophen ‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) and 50 ± 20 S cm−1 for poly(3‐hexyl)thiophene (P3HT). Interband optical absorption of the polymers in the doped state is drastically reduced, making these highly conductive films transparent in the visible range. The dopants within the porous polymer matrix are partially crosslinked via a silane self‐polymerization mechanism that makes the samples very stable in vacuum and nonpolar environments. The mechanism of SAM‐induced conductivity is believed to be based on protonic doping by the free silanol groups available within the partially crosslinked SAM network incorporated in the polythiophene structure. The SAM‐doped polythiophenes exhibit an intrinsic sensing effect: a drastic and reversible change in conductivity in response to ambient polar molecules, which is believed to be due to the interaction of the silanol groups with polar analytes. The reported electronic effects point to a new attractive route for doping conjugated polymers with potential applications in transparent conductors and molecular sensors. Doping conjugated polythiophenes with silane‐based molecules capable of forming self‐assembled monolayers results in an increase in the electrical conductivity by up to six orders of magnitude. Additionally, the interband optical absorption becomes significantly reduced, making the polymer films transparent in the visible range. These results point to a new attractive route for doping conjugated polymers with potential applications in transparent conductors and molecular sensors.