The impact of side chain elongation from the Y6 to Y6-12 acceptor in organic solar cells: a fundamental study from molecules to devices

Abstract

In order to contribute to the establishment of clear structure–property relationships of non-fullerene acceptors in organic solar cells, we focus here on the rising star Y6 acceptor to assess the impact of elongating the inner side chain from 8 to 12 carbon atoms via a joint theoretical and experimental characterization study combining DFT calculations, UV-visible spectroscopy, atomic force microscopy (AFM) analysis and device fabrication and characterization. The originality of the present work is to compare Y6 and Y6-12 under the same experimental conditions in order to make more transparent the added benefits of using longer saturated side chains. Although the optoelectronic properties of the blends with the prototypical PM7 donor polymer are not strongly impacted by the side chain length, the morphology of the films is deeply modified as a function of the nature of the solvent used for their processing, which affects in turn the performance of the devices.