Effect of Alkyl Side Chains of Conjugated Polymer Donors on the Device Performance of Non-Fullerene Solar Cells

The influence of the chemical: structure of conjugated polymers on the nanophase separation and device performance in fullerene-based solar cells has been widely studied, while this is, less investigated in non-fullerene solar cells. In this work, we design three conjugated polymers With-different length of side chains, and we find that the length of side chains has little influence on the quantum efficiencies of non-fullerene solar cells. As a comparison, the length of side chains has a significant effect on the quantum efficiencies of fullerene-based solar cells. This indicates that morphology of the blended thin films in non-fullerene solar, cells is rather independent of the length of the donor side chains; and the mechanism for morphology evolution in the non-fullerene system is completely different from that in the fullerene system. Our conclusion is confirmed by a variety of advanced characterization techniques. The studies reveal that in blended thin films based on the non-fullerene material the donor polymers with different side chains have a Similar coherence length of pi-pi stacking, crystal size and domain purity, giving rise-to similar internal quantum efficiency and power conversion efficiency of the solar cells.