Solution–Doped Donor–Acceptor Copolymers Based on Diketopyrrolopyrrole and 3, 3'–Bis (2–(2–(2–Methoxyethoxy) Ethoxy) ethoxy)–2, 2'–Bithiophene Exhibiting Outstanding Thermoelectric Power Factors with p–Dopants

Journal Article · 31 October 2023 · Advanced Functional Materials

DOI: https://doi.org/10.1002/adfm.202309646 · OSTI ID:2309763

Mukhopadhyaya, Tushita ^[1]; Wagner, Justine ^[1]; Lee, Taein D. ^[1]; Ganley, Connor ^[1]; Tanwar, Swati ^[1]; Raj, Piyush ^[1]; Li, Lulin ^[1]; Song, Yunjia ^[1]; Melvin, Sophia J. ^[1]; Ji, Yuyang ^[1]; Clancy, Paulette ^[1]; Barman, Ishan ^[1]; Thon, Susanna ^[1]; Klausen, Rebekka S. ^[1]; Katz, Howard E.  ^[1]

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1. Johns Hopkins University, Baltimore, MD (United States)

The design of polymeric semiconductors exhibiting high electrical conductivity (σ) and thermoelectric power factor (PF) will be vital for flexible large-area electronics. In this work, four polymers based on diketopyrrolopyrrole (DPP), 2,3-dihydrothieno[3,4-b][1,4]dioxine (EDOT), thieno[3,2-b]thiophene (TT), and 3, 3'-bis (2-(2-(2-methoxyethoxy) ethoxy) ethoxy)-2, 2'-bithiophene (MEET) are investigated as side-chains, with the MEET polymers newly synthesized for this study. These polymers are systematically doped with tetrafluorotetracyanoquinodimethane ( F₄TCNQ), CF3SO3H, and the synthesized dopant Cp(CN)₃-(COOMe)₃, differing in geometry and electron affinity. The DPP-EDOT-based polymer containing MEET as side-chains exhibits the highest conductivity (σ) ≈700 S cm–1 in this series with the acidic dopant (CF₃SO₃H). This polymer also shows the lowest oxidation potential by cyclic voltammetry (CV), the strongest intermolecular interactions evidenced by differential scanning calorimetry (DSC), and has the most oxygen-based functionality for possible hydrogen bonding and ionic screening. Other polymers exhibit high σ ≈300–500 S cm–1 and power factor up to 300 µW m^–1 K^–2. The mechanism of conductivity is predominantly electronic, as validated by time-dependent conductance studies and transient thermo voltage monitoring over time, including for those doped with the acid. Furthermore, these materials maintain significant thermal stability and air stability over ≈6 weeks. Density functional theory calculations reveal molecular geometries and inform about frontier energy levels. Raman spectroscopy, in conjunction with scanning electron microscopy (SEM-EDS) and x-ray diffraction, provides insight into the solid-state microstructure and degree of phase separation of the doped polymer films. Infrared spectroscopy enables this study to further quantify the degree of charge transfer from polymer to dopant.

• Research Organization: Johns Hopkins University, Baltimore, MD (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
• Grant/Contract Number: FG02-07ER46465; 1708245; 2107360; OAC 1920103
• OSTI ID: 2309763
• Journal Information: Advanced Functional Materials, Vol. 34, Issue 7; ISSN 1616-301X
• Publisher: WileyCopyright Statement
• Country of Publication: United States
• Language: English