Publication date: 22nd July 2026
Solution-processed molecular doping is a promising strategy to improve charge transport in organic semiconductors, but the relationship between dopant loading, thermal stability, and depth-dependent film morphology remains insufficiently understood. In this work, PM6 polymer thin films were doped with F4TCNQ and F6TCNNQ, and their electrical conductivity and vertical morphology were investigated as a function of dopant loading and thermal annealing.
Neutron reflectometry (NR) reveals that increasing dopant concentration leads to modest film densification and surface smoothing, while the fitted scattering length density remains close to that of pristine PM6 at dopant loadings of 1, 3, and 5%. These results indicate no clear evidence of macroscopic vertical stratification within the sensitivity of the measurements, suggesting that the doped films retain a largely stable depth profile after solution processing. Conductivity measurements after stepwise thermal annealing up to 150 °C were used to evaluate changes in doping efficiency and possible thermal dedoping. Complementary NR measurements on pristine PM6 show only minor changes in thickness and roughness after annealing to 150 °C, indicating that the PM6 matrix itself is vertically stable under these conditions. Therefore, annealing-induced changes in conductivity are more likely associated with local molecular rearrangement, dopant-polymer interactions, or changes in crystalline packing rather than large-scale vertical phase segregation.
Ongoing X-ray scattering and complementary thin-film characterization will further correlate conductivity evolution with molecular packing and nanoscale texture. Overall, this work provides a depth-resolved framework for evaluating dopant retention, morphology stability, and thermal robustness in solution-processed donor polymers for organic electronic applications.
The authors gratefully acknowledge funding support from the National Science and Technology Council (NSTC), Taiwan.
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