Simple oxime functionalized fluorene polymers for organic solar cells†

Conjugated polymers with simple chemical structures are attractive for the design of high efficiency, wide bandgap (WBG) donor materials used in non-fullerene organic solar cells. Fluorene is one of the most common structures in organic opto-electronic materials. It is herein used, for the first time, functionalized with the oxime group to construct the acceptor unit of D–A polymer donors with a BDT donor unit. The polymers, PBFO-H and PBFO-F, had low-lying HOMOs with a wide bandgap of 2.08 eV and are soluble in chloroform for easy processing. Organic solar cells were constructed using the polymers and a non-fullerene Y6 acceptor. The fluorinated polymer (PBFO-F) had better photovoltaic properties over the non-fluorinated polymer overall, with J_SC, V_OC, and FF values of 23.17 mA cm⁻², 0.84 V, and 55.2%, respectively, and a high PCE of 10.71%. These results demonstrate that fluorene is promising in constructing acceptor units for D–A wide bandgap polymers.