Toward Low Energetic Disorder in Organic Solar Cells: The Critical Role of Polymer Donors

Compared with those of inorganic and perovskite solar cells, the power conversion efficiencies of organic solar cells (OSCs) are severely limited by a large energetic disorder. However, the origin of energetic disorder for OSCs remains poorly understood. Herein, we systematically investigate the energetic disorder in representative OSCs and the effect of both the acceptors and polymer donors by combining atomistic molecular dynamics simulations with density functional theory calculations. The results indicate that regardless of whether the OSCs are based on fullerene or acceptor-donor-acceptor (A-D-A) acceptors, the energetic disorder in the ionization potentials of the polymer donors is significantly larger than that in the electron affinities of the acceptors. Moreover, the energetic disorder of the donors matched with the fullerene acceptors is noticeably greater than that of the donors matched with the A-D-A acceptors. This implies that, different from our intuition, the reduction in the energetic disorder from the fullerene-based to A-D-A acceptor-based OSCs is primarily attributed to the change in the polymer donors rather than the acceptors. This work underscores the vital importance of optimizing polymer donors toward low energetic disorder for high-efficiency OSCs.