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

• Published in: Advanced functional materials 2024-02, Vol.34 (7), p.n/a
• Main Authors: Mukhopadhyaya, Tushita, Wagner, Justine, Lee, Taein D., Ganley, Connor, Tanwar, Swati, Raj, Piyush, Li, Lulin, Song, Yunjia, Melvin, Sophia J., Ji, Yuyang, Clancy, Paulette, Barman, Ishan, Thon, Susanna, Klausen, Rebekka S., Katz, Howard E.
• Format: Article
• Language: English
• Subjects: Acidic oxides; Charge transfer; conducting polymer; Copolymers; Density functional theory; diketopyrrolopyrrole; dopant; Dopants; Electrical resistivity; Electron affinity; Energy levels; Hydrogen bonding; Infrared spectroscopy; MATERIALS SCIENCE; Oxidation; Phase separation; Polymer films; Polymers; Power factor; Raman spectroscopy; Spectrum analysis; Synthesis; Thermal stability; thermoelectric; Thermoelectricity; Time dependence; Triflic acid
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202309646

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. 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. Four polymers based on diketopyrrolopyrrole (DPP), ethylenedioxythiophene (EDOT), and methoxyethoxyethoxythiophene (MEET) are doped with F4TCNQ, CF3SO3H, and the synthesized dopant Cp(CN)3‐(COOMe)3. The EDOT‐MEET combination exhibits the highest σ ≈700 S cm‐1, with CF3SO3H, lowest oxidation potential, and strongest intermolecular interactions. Thermoelectric power factors of 100–300 µW m‐1 K‐2 are also obtained.