Perylene diimide based all small-molecule organic solar cells: Impact of branched-alkyl side chains on solubility, photophysics, self-assembly, and photovoltaic parameters

Perylene diimide derivatives have been under intense investigation to replace fullerenes as the electron accepting component in organic photovoltaics, with molecular complexity continuing to grow. Simple alkyl-substituted perylene diimide monomers at the imide nitrogen position, however, have not been extensively investigated. Herein we demonstrate that subtle alkyl-substitutions at the imide-nitrogen position lead to significant changes in solubility, thin-film self-assembly and optical properties. When blended with a small-molecule donor to form all small-molecule, fullerene-free, solution processed organic solar cells, we show that the photovoltaic device performance and consistency can be tuned via alkyl-chain modifications. In addition we have simplified the device fabrication process by utilizing a silver cathode coupled with a small-molecule-ionic interlayer and achieved comparable performance to devices fabricated with a traditional Ca/Al cathode. (C) 2016 Elsevier B.V. All rights reserved.