Unravelling the mechanism of processing protocols induced microstructure evolution on polymer thermoelectric performance

Processing protocols definitely impact polymer microstructure evolution and thermoelectric (TE) performance; however, in-depth understanding of molecular mechanism is still a challenge. Here, the mechanism of the effects of solution- and melt-processing protocols on polymer microstructure evolution and TE performance has been unraveled, where a semicrystalline poly(3-hexylthiophene) (P3HT) is chosen as a model system. The phase separations between crystallites and amorphous regions are more pronounced for melt-processed films, and solution-processed films display enlarged conjugation length and higher degree of solid-state ordering. In crystalline domains, solution-processed films reveal a completely edge-on structure, while melt-processed exhibit a co-existing of edge-on and face-on crystallites. Additionally, solution-aging strengthens aggregation and phase separation, but has little effect on conjugation length and crystalline texture. Finally, a multiphase semicrystalline model, based on crystalline texture and phase separation, is applied.