Enhanced efficiency of polymer solar cells via simple fluorination on the π-bridge of polymer donors

In this contribution, a novel fluorinated polymer based on the well-known J52, using the newly developed 3-fluorothiophene as π bridges on the conjugated main chain, named J52-FTh, was synthesized and was used as polymer solar cells (PSCs) donor material. The effects of fluorinated π bridge on the polymer's thermal stability, light absorption, energy level, molecular configuration and photovoltaic performance were systematically studied. It demonstrated that J52-FTh exhibited an enhanced absorption, a narrower optical band gap, a low-lying the highest occupied molecular orbitals (HOMO) energy level and better coplanar compared with J52 without any fluorine substituent on its π bridges. The non-fullerene PSCs based on J52-FTh:ITIC (1:0.8, w/w) achieved a high PCE of 13.32% with a VOC of 0.92 V, a JSC of 21.29 mA cm−2 and an FF of 68%, which was much better than the PSCs based on J52:ITIC with a PCE of 5.51%. The results indicated that fluorination on the polymer's main chain was a simple and efficient strategy toward high efficiency.