A rare case of iodinated non-fullerene acceptors for high-performance organic solar cells without post-treatments

Conventional halogenations such as fluorination, chlorination and bromination on non-fullerene acceptors (NFAs) generally contribute to a dramatic improvement in overall photovoltaic performance of organic solar cells (OSCs). Despite the potentially enhanced intermolecular interaction caused by iodine atoms with increased polarizability, iodinated NFAs are quite rare due to the high-reactive activity of iodine. Here, an iodinated acceptor (CH45) is constructed, rendering a first-class efficiency of 18.15% for OSCs without any extra post-treatments, attributed to the enlarged molecular polarizability and dielectric constant, and further reduced exciton binding energy of CH45. Moreover, the working mechanism of 1-chloronaphthalene additive to greatly improve fill factors of CH45-based OSCs is also revealed at single-crystal levels. By successfully establishing such a rarely iodinated but high-performance molecular platform, more delicately iodinated light-harvesting molecules with unexpected properties (such as significantly enhanced intermolecular non-covalent actions) will be inspired to further achieve high-efficiency OSCs without tedious post-treatments.