Polythiophenes for organic solar cells with efficiency surpassing 17%

Polythiophenes (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.