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

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Abstract

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
DOIs
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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