Polythiophenes for organic solar cells with efficiency surpassing 17%

Context & scaleThe development of polythiophenes (PTs) is an important topic in the field of organic optoelectronics due to their intrinsic structural simplicity and facile synthesis. However, the device performance of PTs in non-fullerene organic solar cells (OSCs) is rather poor due to unmatched energy levels and unfavorable active layer morphology. To date, the highest power conversion efficiency (PCE) of PT-based OSCs in the literature is only 13.65%. In this work, we report the first polythiophene that exhibits over 17% efficiency, which is the new efficiency record of PT-based OSCs. Moreover, our work reveals the crucial role of polymer solubility and thermodynamic miscibility in determining the morphology and device performance of PT:non-fullerene systems, which provides design guidelines for more efficient PT-based OSCs. This work represents a significant advance in the field of OSCs, even across the entire field of organic electronics.Highlights•Polythiophenes for high-performance organic solar cells are developed•A record efficiency of 17.2% is achieved for polythiophene solar cells•Design guidelines are unraveled for polythiophenes to realize high efficiencySummaryPolythiophenes (PTs) are promising electron donors for organic solar cells (OSCs) due to their low production cost. However, the device performance of PTs in OSCs is rather poor due to unmatched energy levels and unfavorable active layer morphology. Herein, we report a set of new PTs (P5TCN-Fx) with cyano-group substitutions and varied fluorination degrees to achieve high-efficiency OSCs. The incorporation of the cyano-group endows the new PTs with deep-lying energy levels, and backbone fluorination leads to strong interchain interaction, improved polymer crystallinity, and appropriate thermodynamic miscibility with the prevailing acceptor Y6 for the new PTs. As a result, multiple PTs have offered over 16% efficiency in binary OSCs. Moreover, a prominent PCE of 17.2% has been obtained by P5TCN-F25 via ternary blend design, which is the new efficiency record and represents a big breakthrough for PT-based OSCs. This work opens a promising avenue to achieve high-performance OSCs from low-cost materials.Graphical abstract