Ordering structure control of polythiophene-based donors for High-Efficiency organic solar cells

The development of high-performance organic solar cells (OSCs) from the low-cost and highly scalable polythiophene family has been garnering a fast-growing interest for their commercialization to be viable. By introducing different difluorobithiophene (2FT) content into thiophene -dithienylthiazolothiazole (TTz)-based polymer backbone, we have developed TTz-based polymers (PTTz, PTTz-2FT10, PTTz-2FT20, and PTTz-2FT30) as the polythiophene derivative donors, processing down-shifted energy levels with an improved pre-aggregation property and a lower miscibility with m-BTP-PhC6 acceptor. When blended with the m-BTP-PhC6 acceptor, the ordering structures (i.e., crystallinity and backbone orientation) in the blends can be altered. Furthermore, we demonstrate that the blend using PTTz-2FT20 has a well-balanced bimodal molecular distribution with more regulated face-on and edge-on crystallites, resulting in the best power conversion efficiency (PCE) of 16.18% among current OSC studies. Moreover, a notable PCE of 17.13% is obtained in the PTTz-2FT20 via ternary blend, which is one of the highest values reported for polythiophene-based OSCs to date. Therefore, our results provide new insights on the operating mechanism and morphology (orientation) -performance (OSC output) relationship in polythiophene-based OSCs, which are useful for designing high-performance polythiophene donors.