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On the Origin of Seebeck Coefficient Inversion in Highly Doped Conducting Polymers
Author(s) -
Xu Kai,
Ruoko TeroPetri,
Shokrani Morteza,
Scheunemann Dorothea,
Abdalla Hassan,
Sun Hengda,
Yang ChiYuan,
Puttisong Yuttapoom,
Kolhe Nagesh B.,
Figueroa José Silvestre Mendoza,
Pedersen Jonas O.,
Ederth Thomas,
Chen Weimin M.,
Berggren Magnus,
Jenekhe Samson A.,
Fazzi Daniele,
Kemerink Martijn,
Fabiano Simone
Publication year - 2022
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.202112276
Subject(s) - seebeck coefficient , materials science , condensed matter physics , doping , thermoelectric effect , thermoelectric materials , density functional theory , electrical resistivity and conductivity , raman spectroscopy , polymer , chemical physics , thermal conductivity , optoelectronics , computational chemistry , physics , thermodynamics , chemistry , optics , composite material , quantum mechanics
A common way of determining the majority charge carriers of pristine and doped semiconducting polymers is to measure the sign of the Seebeck coefficient. However, a polarity change of the Seebeck coefficient has recently been observed to occur in highly doped polymers. Here, it is shown that the Seebeck coefficient inversion is the result of the density of states filling and opening of a hard Coulomb gap around the Fermi energy at high doping levels. Electrochemical n‐doping is used to induce high carrier density (>1 charge/monomer) in the model system poly(benzimidazobenzophenanthroline) (BBL). By combining conductivity and Seebeck coefficient measurements with in situ electron paramagnetic resonance, UV–vis–NIR, Raman spectroelectrochemistry, density functional theory calculations, and kinetic Monte Carlo simulations, the formation of multiply charged species and the opening of a hard Coulomb gap in the density of states, which is responsible for the Seebeck coefficient inversion and drop in electrical conductivity, are uncovered. The findings provide a simple picture that clarifies the roles of energetic disorder and Coulomb interactions in highly doped polymers and have implications for the molecular design of next‐generation conjugated polymers.