Polaron interfacial entropy as a route to high thermoelectric performance in DAE-doped PEDOT:PSS films

Enhancing the thermoelectric transport properties of conductive polymer materials has been a long-term challenge, in spite of the success seen with molecular doping strategies. However, the strong coupling between the thermopower and the electrical conductivity limits thermoelectric performance. Here, we use polaron interfacial occupied entropy engineering to break through this intercoupling for a PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate)) thin film by using photochromic diarylethene (DAE) dopants coupled with UV-light modulation. With a 10-fold enhancement of the thermopower from 13.5 μV K^-1 to 135.4 μV K^-1 and almost unchanged electrical conductivity, the DAE-doped PEDOT:PSS thin film achieved an extremely high power factor of 521.28 μW m^-1 K^-2 from an original value of 6.78 μW m^-1 K^-2. The thermopower was positively correlated with the UV-light intensity but decreased with increasing temperature, indicating resonant coupling between the planar closed DAE molecule and PEDOT. Both the experiments and theoretical calculations consistently confirmed the formation of an interface state due to this resonant coupling. Interfacial entropy engineering of polarons could play a critical role in enhancing the thermoelectric performance of the organic film.