Publication date: 21st July 2025
Mixed conducting polymers have become attractive for their potential application as active materials in electrochemical devices such as organic electrochemical transistors (OECTs).
This contribution will highlight our ongoing research on electrochemical doping behavior of n-type polymers, namely the donor-acceptor copolymer poly[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)[P(NDI2OD-T2)] [1], [2], [3] and its derivatives modified with oligo(ethylene glycol) side chains and selenophene-vinylene-selenophene as donor units [4]. We used an in situ spectroelectrochemical approach to investigate their absorption characteristics with different doping degrees and to identify their redox states during electrochemical doping. We further employed in situ technique to determine the reduction onset potentials through spectral evolution mapping from the neutral in the first reduced state. Compared to conventional cyclic voltammetry, this approach improves the certainty in the onset potential determination of conducting polymers, enabling more accurate estimation of the lowest unoccupied molecular orbital (LUMO) energy levels for their device applications. The glycolated and fluorinated P(NDIEG7-FSVS) exhibited a LUMO energy level of -4.63 eV [4], significantly lower than that of P(NDI2OD-T2) around -4.0 eV [1], [2], [3].
Furthermore, UV-vis-NIR absorption spectroscopy confirms that the redox states of electrochemically doped polymer films can be retained in the solid state [3]. Four-line probe measurements of P(NDI2OD-T2) films with different doping levels showed a characteristic bell-shaped conductivity profile, indicating mixed valence charge transport in the conjugated redox polymer system [3]. For aligned films prepared by blade-coating, conductivity measurements after electrochemical doping reveal anisotropic charge transport behavior, with higher conductivity achieved along the polymer chain direction [2], [3]. This offers a morphology-control strategy for designing high-performance organic electronics.
X.S. and S.L. acknowledge funding by the German Research Foundation (DFG) via Research Training Group GRK 2948. S.W. acknowledge funding support from Agence Nationale de la Recherche (ANR-23-CPJ1-0047-01).
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