N-type semiconducting perylene diimide based molecules for organic solar cells

Core substituted perylene diimides (PDIs) are promising candidates as non-fullerene acceptor materials for organic solar cells. The functionalization of PDIs in the bay positions using chemical groups with different electron donating abilities and with steric hindrance is a versatile tool to modify both the optoelectronic properties and the morphology in the solid state. Herein we present two new PDI based molecules having bulky aromatic substituents linked into the bay positions: PDI-SF with spirobifluorene group and PDI-BSF with bithienyl-spirobifluorene moieties. The high steric hindrance of spirobifluorene reduce the tendency to form aggregates that has been identified as a limiting factor for the photovoltaic performances in PDI based solar cells. The PDI molecules were tested as electron acceptors in bulk heterojunction solar cells with P3HT as electron donor. Power conversion efficiencies (PCE) of 1.58% and 1.18% were obtained for PDI-SF and PDI-BSF devices.