The Effects of Crystallinity on Charge Transport and the Structure of Sequentially Processed F ₄ TCNQ‐Doped Conjugated Polymer Films

Journal Article · Wed Sep 27 00:00:00 EDT 2017 · Advanced Functional Materials

DOI:https://doi.org/10.1002/adfm.201702654· OSTI ID:1395403

Scholes, D. Tyler ^[1]; Yee, Patrick Y. ^[1]; Lindemuth, Jeffrey R. ^[2]; Kang, Hyeyeon ^[1]; Onorato, Jonathan ^[3]; Ghosh, Raja ^[4]; Luscombe, Christine K. ^[3]; Spano, Frank C. ^[4]; Tolbert, Sarah H. ^[5]; Schwartz, Benjamin J.  ^[6]

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1. Department of Chemistry and Biochemistry University of California, Los Angeles Los Angeles CA 90095‐1569 USA
2. Lake Shore Cryotronics Westerville OH 43082 USA
3. Materials Science and Engineering Department University of Washington Seattle WA 98195‐2120 USA
4. Department of Chemistry Temple University Philadelphia PA 19122 USA
5. Department of Chemistry and Biochemistry University of California, Los Angeles Los Angeles CA 90095‐1569 USA, Department of Materials Science and Engineering University of California, Los Angeles Los Angeles CA 90095 USA, California NanoSystems Institute University of California, Los Angeles Los Angeles CA 90095 USA
6. Department of Chemistry and Biochemistry University of California, Los Angeles Los Angeles CA 90095‐1569 USA, California NanoSystems Institute University of California, Los Angeles Los Angeles CA 90095 USA

Abstract The properties of molecularly doped films of conjugated polymers are explored as the crystallinity of the polymer is systematically varied. Solution sequential processing (SqP) was used to introduce 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F ₄ TCNQ) into poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) while preserving the pristine polymer's degree of crystallinity. X‐ray data suggest that F ₄ TCNQ anions reside primarily in the amorphous regions of the film as well as in the P3HT lamellae between the side chains, but do not π‐stack within the polymer crystallites. Optical spectroscopy shows that the polaron absorption redshifts with increasing polymer crystallinity and increases in cross section. Theoretical modeling suggests that the polaron spectrum is inhomogeneously broadened by the presence of the anions, which reside on average 6–8 Å from the polymer backbone. Electrical measurements show that the conductivity of P3HT films doped by F ₄ TCNQ via SqP can be improved by increasing the polymer crystallinity. AC magnetic field Hall measurements show that the increased conductivity results from improved mobility of the carriers with increasing crystallinity, reaching over 0.1 cm ² V ⁻¹ s ⁻¹ in the most crystalline P3HT samples. Temperature‐dependent conductivity measurements show that polaron mobility in SqP‐doped P3HT is still dominated by hopping transport, but that more crystalline samples are on the edge of a transition to diffusive transport at room temperature.

• Sponsoring Organization: USDOE
• Grant/Contract Number: DE‐AC02‐76SF00515
• OSTI ID: 1395403
• Journal Information: Advanced Functional Materials, Journal Name: Advanced Functional Materials Vol. 27 Journal Issue: 44; ISSN 1616-301X
• Publisher: Wiley Blackwell (John Wiley & Sons)
• Country of Publication: Germany
• Language: English