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N-Type Organic Thermoelectrics of Donor-Acceptor Copolymers: Improved Power Factor by Molecular Tailoring of the Density of States

Liu, J., Ye, G., van der Zee, B., Dong, J., Qiu, X., Liu, Y., Portale, G., Chiechi, R. C. & Koster, L. J. A., 2-Nov-2018, In : Advanced materials. 30, 44, 9 p., 1804290.

Research output: Contribution to journalArticleAcademicpeer-review

It is demonstrated that the n-type thermoelectric performance of donor-acceptor (D-A) copolymers can be enhanced by a factor of >1000 by tailoring the density of states (DOS). The DOS distribution is tailored by embedding sp(2)-nitrogen atoms into the donor moiety of the D-A backbone. Consequently, an electrical conductivity of 1.8 S cm(-1) and a power factor of 4.5 mu W m(-1) K-2 are achieved. Interestingly, an unusual sign switching (from negative to positive) of the Seebeck coefficient of the unmodified D-A copolymer at moderately high dopant loading is observed. A direct measurement of the DOS shows that the DOS distributions become less broad upon modifying the backbone in both pristine and doped states. Additionally, doping-induced charge transfer complexes (CTC) states, which are energetically located below the neutral band, are observed in DOS of the doped unmodified D-A copolymer. It is proposed that charge transport through these CTC states is responsible for the positive Seebeck coefficients in this n-doped system. This is supported by numerical simulation and temperature dependence of Seebeck coefficient. The work provides a unique insight into the fundamental understanding of molecular doping and sheds light on designing efficient n-type OTE materials from a perspective of tailoring the DOS.

Original languageEnglish
Article number1804290
Number of pages9
JournalAdvanced materials
Volume30
Issue number44
Publication statusPublished - 2-Nov-2018

    Keywords

  • donor-acceptor copolymers, electrical conductivity and density of states, n-type doping, solution processing, FIELD-EFFECT TRANSISTORS, DOPING EFFICIENCY, HIGH-MOBILITY, SEMICONDUCTORS, POLYMER, DOPANT, CONDUCTIVITY, DEVICES, DESIGN, ORDER

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