Revealing the Effect of the Side Chain on the Adsorption Configuration of the Asymmetric Interface Molecule (PFN-Br) on the Acceptor (Y6) Interface

The side chains of the interface layer materials of organic solar cells play an essential role in promoting dissolution, self-assembly, and energy level regulation. Still, the formation mechanism of these theories needs to be further studied. Theoretical calculation methods can predict and analyze the self-assembly process. In this paper, the influence of side chains on the adsorption process of the poly[(9,9-bis(3'-(N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioct-ylfluorene)]dibromide (PFN-Br) molecule onto the active layer substrate was investigated using theoretical computational methods. The weak interaction between the substrate and the PFN-Br molecule makes it tend to form a more stable positive structure, forming a stronger interface dipole electric field and more effectively reducing the work function of the active layer, which is conducive to charge extraction and hindering hole transport. Subsequent experiments found that a soaking strategy enhances the formation of beneficial structures and improves charge extraction, paving the way for new molecular design and device optimization.