Reducing Voltage Losses in Organic Solar Cells Based on Fluorinated Acceptors

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 (Voc) of the solar cells, thereby limiting their overall performance. In this study, we investigate the limitation of Voc in organic solar cells based on fluorinated acceptors. Our investigation reveals that the reduced Voc can be attributed to increased voltage losses (Vloss), primarily arising from more significant non-radiative voltage losses originating from a decline in the external quantum efficiency of electroluminescence (EQEEL). Furthermore, we establish that the reduced EQEEL is a result of deteriorated molecular packing, which leads to an elevated reorganization energy. To address the high Vloss 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.