Title: Microstructure and heteroatom dictate the doping mechanism and thermoelectric properties of poly(alkyl-chalcogenophenes)

Abstract

Heteroatom substitution can favorably alter electronic transport in conductive polymers to improve their thermoelectric performance. This study reports the spectroscopic, structural, and thermoelectric properties of poly(3–(3′,7′-dimethyloctyl) chalcogenophenes) or P3RX doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), where the heteroatom [X = thiophene (T), selenophene (Se), tellurophene (Te)], the doping methodology, and extent of doping are systematically varied. Spectroscopic measurements reveal that while all P3RX polymers are appreciably doped, the doping mechanism is inherently different. Poly(3-hexylthiophene) (P3HT, used as a control) and poly(3–(3′,7′-dimethyloctyl)tellurophene) (P3RTe) are doped primarily via integer charge transfer (ICT), whereas poly(3–(3′,7′-dimethyloctyl)selenophene) (P3RSe) and poly(3–(3′,7′-dimethyloctyl)thiophene) (P3RT) are doped via charge transfer complex (CTC) mechanisms. Despite these differences, all polymers saturate with roughly the same number of F4TCNQ counterions (1 dopant per 4 to 6 heterocycles), reinforcing the idea that the extent of charge transfer varies with the doping mechanism. Grazing incidence wide-angle x-ray scattering measurements provide insight into the structural driving forces behind different doping mechanisms—P3RT and P3RSe have similar microstructures in which F4TCNQ intercalates between the π-stacked backbones resulting in CTC doping (localized carriers), while P3HT and P3RTe have microstructures in which F4TCNQ intercalates in the alkyl side chain region, giving rise to ICT doping (delocalized carriers). These structural and spectroscopic observations shedmore » light on why P3HT and P3RTe obtain electrical conductivities ca. 3 S/cm, while P3RT and P3RSe have conductivities <10−3 S/cm under the same thin film processing conditions. Ultimately, this work quantifies the effects of heteroatom, microstructural ordering, extent of doping, and doping mechanism, thereby providing rational guidance for designing future thermoelectric polymer-dopant systems.« less

Authors:

Gordon, Madeleine P. ^[1]; Gregory, Shawn A. ^[2]; Wooding, Jamie P. ^[2]; Ye, Shuyang ^[3]; Su, Gregory M.  ^[4];

• Search DOE PAGES for author "Su, Gregory M."
• Search DOE PAGES for ORCID "0000-0001-7495-8041"

Seferos, Dwight S. ^[3]; Losego, Mark D.  ^[2];

• Search DOE PAGES for author "Losego, Mark D."
• Search DOE PAGES for ORCID "0000-0002-9810-9834"

Urban, Jeffrey J.  ^[5];

• Search DOE PAGES for author "Urban, Jeffrey J."
• Search DOE PAGES for ORCID "0000-0003-4909-2869"

Yee, Shannon K.  ^[2];

• Search DOE PAGES for author "Yee, Shannon K."
• Search DOE PAGES for ORCID "0000-0002-1119-9938"

Menon, Akanksha K.  ^[2]

• Search DOE PAGES for author "Menon, Akanksha K."
• Search DOE PAGES for ORCID "0000-0003-1979-507X"

---

+ Show Author Affiliations

1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Foundry; Univ. of California, Berkeley, CA (United States)
2. Georgia Institute of Technology, Atlanta, GA (United States)
3. Univ. of Toronto, ON (Canada)
4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division & Advanced Light Source (ALS)
5. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Foundry

Publication Date:

Mon Jun 07 00:00:00 EDT 2021

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); US Department of the Navy, Office of Naval Research (ONR); US Department of Education; National Science Foundation (NSF)

OSTI Identifier:

1807521

Alternate Identifier(s):

OSTI ID: 1786856

Grant/Contract Number:  

AC02-05CH11231; N00014-19-1-2162; P200A180075; ECCS-1542174

Resource Type:

Accepted Manuscript

Journal Name:

Applied Physics Letters

Additional Journal Information:

Journal Volume: 118; Journal Issue: 23; Journal ID: ISSN 0003-6951

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; doping; chemical compounds; x-ray scattering spectroscopy; ions and properties; thin films; electronic transport; thermoelectric effects; thermoelectric devices; electrical conductivity; polymers