Reducing voltage losses in organic solar cells based on fluorinated acceptors.

• Acceptor fluorination leads to increased voltage losses in organic solar cells. • The increased voltage loss is associated with increased reorganization energy. • A side chain modification strategy is proposed to address the voltage loss issue. Acceptor fluorination is a commonly employed molecular modification strategy aimed at enhancing the quantum efficiency and charge carrier transport properties of organic solar cells. However, this approach often leads to a significant reduction in the open-circuit voltage (V oc) of the solar cells, thereby limiting their overall performance. In this study, we investigate the limitation of V oc in organic solar cells based on fluorinated acceptors. Our investigation reveals that the reduced V oc can be attributed to increased voltage losses (V loss), primarily arising from more significant non-radiative voltage losses originating from a decline in the external quantum efficiency of electroluminescence (EQE EL). Furthermore, we establish that the reduced EQE EL is a result of deteriorated molecular packing, which leads to an elevated reorganization energy. To address the high V loss and limited performance observed in solar cells utilizing fluorinated acceptors, we propose a strategy involving acceptor side-chain modifications. These results provide new insights into enhancing the performance of organic solar cells. [ABSTRACT FROM AUTHOR]