Polythiophene (PTh) is an important conjugated polymer for its simple structure, high stability, and various optoelectronic properties. However, due to the high oxidation potential, it is challenging for the unsubstituted thiophene to be polymerized and deposited onto insulating substrates in large area.Here, a modified sequential solution polymerization (SSP) method is demonstrated to be applicable for the in-situ preparation of large-area PTh film on either glass or flexible polyethylene terephthalate (PET) substrate. Both FTIR and Raman spectra suggest that the thiophene units in SSP PTh are mainly linked by C α −C α coupling without overoxidation, providing tight intermolecular π−π stacking in the solid state. Besides, the PTh film shows blue/red color when in doped/neutral state, which can be manipulated either chemically or electrochemically, thus having great potential in reversible chemochromism, electrochromism, or sensor applications.

Random conjugated terpolymers (RCTs) not only promote great comprehension and realization for the state-of-the-art highly effective non-fullerene organic solar cells (OSCs) but also offer a simple and practical synthetic strategy. However, the photovoltaic properties of RCTs yet lagged behind that of the donor−acceptor (D−A) alternating copolymer, especially in additivefree devices. Hence, we developed two feasible "double-acceptor-type" random conjugated terpolymers, PBDB-TAZ20 and PBDB-TAZ40. The additive-free OSCs based on PBDB-TAZ20:ITIC and PBDB-TAZ40:ITIC exhibit decent efficiencies of 12.34 and 11.27%, respectively, which both surpass the PBDB-T:ITIC-based device. For RCTs, the reasonably weakened crystallinity and the reduced phase separation degree are demonstrated to help in improving charge transport, reducing bimolecular recombination, and thus enhancing the photovoltaic performance of additive-free OSCs. The results imply that adding a third moiety into the D−A polymer donors provides a simple but efficient synthetic approach for high-performance OSCs.

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