Fluorination or Not in Small Molecule Solar Cells: Achieving a Higher Efficiency with Halogen‐Free End Group

• Published in: Chemistry : a European journal 2024-12, Vol.30 (71), p.e202403341-n/a
• Main Authors: Chen, Yao, Tian, Gengsui, Huang, Peihao, Hu, Dingqin, Xiao, Zeyun
• Format: Article
• Language: English
• Subjects: Efficiency; Electron mobility; Energy conversion efficiency; Fluorination; Fluorine; Halogenation; Miscibility; Mixtures; Organic Solar Cells; Photovoltaic cells; Small Molecule Donor; Solar cells
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.202403341

Fluorination is an efficient strategy for improving organic solar cells (OSCs) efficiency, particularly by fluorinating the end group of emerging nonfullerene acceptors. Here, the fluorination effect was investigated by using small molecule donors with fluorine‐free (SBz) and fluorinated (SBz‐F) end groups, paired with the emerging nonfullerene acceptor Y6. Interestingly and unexpectedly, fluorination of the end group negatively affects OSCs efficiency, with fluorine‐free SBz:Y6 OSCs achieving a higher power conversion efficiency (PCE) of 11.05 % compared to the fluorine‐containing SBz‐F:Y6 blends (PCE=9.61 %). Analysis of space‐charge limited currents reveals lower and unbalanced hole/electron mobility in SBz‐F:Y6 compared to the SBz:Y6 blends. These findings are further supported by charge recombination dynamics and donor‐acceptor miscibility analyses. Two readily accessible and scalable end groups for small molecule donors are developed. The resulting fluorine‐free SBz and fluorine‐containing SBz−F were blended with Y6 for small molecule organic solar cells (SM‐OSCs). Surprisingly, the fluorine‐containing SBz−F:Y6 OSCs exhibit a lower efficiency than that of the SBz:Y6 OSCs (9.61 % vs 11.05 %).