Simple Approach for Synthesizing a Fluorinated Polymer Donor Enables Promoted Efficiency in Polymer Solar Cells

In this contribution, we used a practical method to synthesize 3-fluorothiophene as π-bridge units on the polymer backbone via constructing 3-fluoro-2-iodothiophene to decrease synthesis steps and lower costs. Fluorine atoms introduced into the polymer backbone can improve polymer planarity, packing, crystallinity, and hole mobility via extensive noncovalent interactions such as F–H, F–Cl, F–S, and F−π. When compared to the analogue PBZ-Cl without any fluorine substituent on the thiophene unit, our fluorinated polymer J52ClF exhibited red-shifted absorption of roughly 42 nm with a narrower band gap (Egopt) of 1.82 eV, a low-lying highest occupied molecular orbital (HOMO) energy level, and a highly coplanar molecular configuration in the backbone. The optimal device based on J52ClF:IT-4F achieved a desired power conversion efficiency (PCE) of 14.59%, a VOC of 0.93 V, a JSC of 22.67 mA cm–2, a fill factor (FF) of 69.22%, and an Eloss of 0.57 V, all of which were significantly superior to those of PBZ-Cl:IT-4F (PCE = 9.7%). It demonstrated that fluorinating π-conjugated bridges utilizing 3-fluoro-2-iodothiophene is a practical strategy that deserves greater attention for increasing photovoltaic performance.