A systematic investigation on pyridine derived solid additives inducing fibrillar morphology for highly efficient organic solar cells with over 20 % efficiency

A comprehensive understanding of the potential mechanism of the additives-treated photoactive layers is crucial for achieving the desired nanofiber morphology and thus obtaining high performance organic solar cells (OSCs). Herein, three electronegative additives, namely 3,5-dibromopyridine (DBP), 2-methoxy-3,5-dibromopyridine (M-DBP), and 2,6-dimethoxy-3,5-dibromopyridine (DM-DBP), are investigated as solid additives into the D18:L8-BO system. With the increase of the non-covalent interaction between solid additive(s) and active materials, the phase separation and fibrillization of donor and acceptor is distinguishably promoted. However, the device efficiency hasn't been found depending on the fiber length scale as expected, where the charge generation and non-radiative loss are sacrificed. On the contrary, it is found partial fibrillization of active layer treated by 5 mg/ml M-DBP yields the optimal performance, i.e., 19.18 % for binary blend, and 20.07 % for ternary system. Based on the cutting-edge device results, this study demonstrates a full landscape on active layer morphology optimization.