The effect of molecular weight of a series of conjugated polymers (CPs) on the doping efficiency, electrical conductivity, and related thermoelectric properties of doped CPs is studied. Low (L), medium (M), and high (H) molecular weight batches of PDFD-T polymers, based on difluorobenzothiadiazole and dithienosilole moieties, are synthesized and denoted as PDFD-T(L), PDFD-T(M), and PDFD-T(H), respectively. Furthermore, to compare the effects of different donor moieties, donor units of PDFD-T(L) are structurally modified from thiophene to thienothiophene (TT) and dithienothiophene (DTT), denoted as PDFD-TT(L) and PDFD-DTT(L), respectively. After doping the CPs with FeCl3, d-PDFD-T(H) exhibits an electrical conductivity of 402.9 S cm−1, which is significantly higher than those of d-PDFD-T(L), d-PDFD-T(M), d-PDFD-TT(L), and d-PDFD-DTT(L). The highest power factor of 101.1 µW m−1 K−2 is achieved through organic thermoelectric devices fabricated using PDFD-T(H). Through various characterizations, it is demonstrated that CPs with a high molecular weight tend to have a high carrier mobility while maintaining their original crystallinity and good charge transport pathways even after doping. Therefore, it is suggested that optimizing the molecular weight of CPs is an essential strategy for maximal power generation from their doped CP films.
S.E.Y and B.K. contributed equally to this work. This research was supported by NRF grants funded by the Korea government (MSIT) (NRF‐2021R1A2C1007304, NRF‐2020R1A2C2014151, NRF‐2018R1A5A1025594, and NRF‐2020R1A5A1019141). This research was also supported by a grant from Priority Research Centers Program (NRF‐2019R1A6A1A11051471) funded by the National Research Foundation of Korea (NRF). GIWAXS experiments at PLS‐II 6D UNIST‐PAL beamline were supported in part by MEST, POSTECH, and UNIST UCRF.S.E.Y and B.K. contributed equally to this work. This research was supported by NRF grants funded by the Korea government (MSIT) (NRF-2021R1A2C1007304, NRF-2020R1A2C2014151, NRF-2018R1A5A1025594, and NRF-2020R1A5A1019141). This research was also supported by a grant from Priority Research Centers Program (NRF-2019R1A6A1A11051471) funded by the National Research Foundation of Korea (NRF). GIWAXS experiments at PLS-II 6D UNIST-PAL beamline were supported in part by MEST, POSTECH, and UNIST UCRF.
