Molecular p-doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is a widely studied model system. Underlying structure–property relationships are poorly understood because processing and doping are often carried out simultaneously. Here, we exploit doping from the vapor phase, which allows us to disentangle the influence of processing and doping. Through this approach, we are able to establish how the electrical conductivity varies with regard to a series of predefined structural parameters. We demonstrate that improving the degree of solid-state order, which we control through the choice of processing solvent and regioregularity, strongly increases the electrical conductivity. As a result, we achieve a value of up to 12.7 S cm–1 for P3HT:F4TCNQ. We determine the F4TCNQ anion concentration and find that the number of (bound + mobile) charge carriers of about 10–4 mol cm–3 is not influenced by the degree of solid-state order. Thus, the observed increase in electrical conductivity by almost 2 orders of magnitude can be attributed to an increase in charge-carrier mobility to more than 10–1 cm2 V–1 s–1. Surprisingly, in contrast to charge transport in undoped P3HT, we find that the molecular weight of the polymer does not strongly influence the electrical conductivity, which highlights the need for studies that elucidate structure–property relationships of strongly doped conjugated polymers.
|Original language||English (US)|
|Number of pages||9|
|State||Published - Oct 11 2017|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Financial support from the Swedish Research Council, the Swedish Research Council Formas, the Knut and Alice Wallenberg Foundation through a Wallenberg Academy Fellowship, and the European Research Council (ERC) under grant agreement no. 637624 is gratefully acknowledged. We are indebted to Prof. Natalie Stingelin and her group for supplying us with some of the P3HT grades used in this study. We thank Michael Chabinyc for insightful discussions on vapor doping, and Anders Mårtensson for recording the AFM images. The Cornell High Energy Synchrotron Source (CHESS) is acknowledged for providing the beam time for the GIWAXS measurements. CHESS is supported by the NSF & NIH/NIGMS via NSF Award DMR-1332208.