Non-Fullerene Organic Solar Cells with 6.1% Efficiency through Fine-Tuning Parameters of the Film-Forming Process

One of the key issues limiting the efficiency of non-fullerene organic solar cells (NF-SCs) is the low electron mobility and strong recombination loss. In this paper, we report an approach of fine-tuning the parameters relative to the film-forming kinetics to increase the power conversion efficiency, which significantly improved from 1.4 up to 6.1%. The film-forming process was judiciously optimized by carefully manipulating the following four parameters: the additive content during film processing, the volume of the host solvent for solvent vapor annealing (SVA), the volume ratio of the additive versus the host solvent for SVA, and the time for SVA. Through such controls, the photocurrent dramatically increased from 5.40 to 12.83 mA/cm(2) and the fill factor from 32.61 to 56.43% as a result of the reduction of the monomolecular and bimolecular loss and the improvement of the electron mobility. These improvements in the electric properties are associated with the reconstruction of the film morphology, i.e., solvent annealing of the as-cast active film leads to the improvement of the phase segregation and the consequent enhancement of the self-aggregation of the blend donor and acceptor molecules in the solar cell active film.