Comparison of two D-A type polymers with each being fluorinated on D and A unit for high performance solar cells

For the purpose of investigating the effect of fluorination position on D-A type conjugated polymer on photophysical and photovoltaic properties, two types of fluorinated polymere are synthesized, HF with fluorination on electron-donating unit and FH with fluorination on electron-accepting unit. Compared to non-fluorinated polymer, fluorinated polymers exhibit deeper HOMO energy levels without change of bandgap and stronger vibronic shoulder in UV-visible absorption, indicating that fluorination enhances intermolecular interaction. HF with fluorinated D unit exhibits well-developed fibril network, low bimolecular recombination and high hole mobility, which lead a high PCE of 7.10% in conventional single-junction solar cells, which is higher than the PCE (6.41%) of FH with fluorinated A unit. Therefore, this result demonstrates that fluorination on electron-donating unit in D-A polymers could be a promising strategy for achieving high performance polymer solar cells.