Modifying side chain of non-fullerene acceptors to obtain efficient organic solar cells with high fill factor

In recent years, the development of non-fullerene acceptor (NFA) has rapidly improved the power conversion efficiency (PCE) of organic solar cells (OSCs). However, there are still many factors restricting the further improvement of PCE, and the low fill factor (FF) value is one of the main reasons. Therefore, it is of great importance to increase FF through designing organic semiconducting materials. In this paper, Y6-eC6-HD is obtained by modifying two kinds of alkyl chains of Y6, because the regulation of the side alkyl chains as one of the effective methods can get proper film morphology which is beneficial for balanced charge transfer and improved FF. Subsequently, the device based on PM6:Y6-eC6-HD can achieve an outstanding PCE of 16.00% with a high FF of 77.32%. Such a high fill factor is higher than that of the most of Y-series molecules. These results indicate that adjusting the side alkyl chains of NFAs is a promising method to enhance the FF and therefore improving the PCE of OSCs.