Precision Fluorine Functionalization in Alkyl Side Chains of Polymer Donors for Highly Efficient Organic Solar Cells

Fluorination of polymer donors has demonstrated considerable potential for boosting the performance of organic solar cells (OSCs). However, achieving optimal performance requires careful management of fluorine levels, as excessive fluorination may adversely affect device efficiency. In this study, we introduce a controlled number of fluorine atoms into the alkyl side chains of polymer donors to optimize their temperature-dependent aggregation and intermolecular interactions. Four polymers (PTF0, PTF1, PTF2, and PTF3) with reduced synthetic complexity and varying levels of fluorine incorporation were synthesized, allowing precise control over their optoelectronic properties. Notably, PTF1, featuring a single fluorine atom, effectively tunes the energy levels and promotes beneficial intermolecular interactions with the corresponding nonfullerene acceptor. Moreover, PTF1 demonstrates enhanced aggregation and crystallinity, leading to efficient charge generation and transport, resulting in binary and ternary OSCs with PCEs of 13.0% and 18.6%, respectively. This study suggests the potential of precise fluorine functionalization in polymer donors as a potent strategy for crafting highly efficient OSCs and provides valuable insights for designing next-generation OSC materials, paving the way for future advancements.