Perylene diimide isomers containing a simple sp³-core for non-fullerene-based polymer solar cells

In order to investigate the effect of the geometries of perylene diimide (PDI)-based small molecules, five different isomers were synthesized by using a cyclohexane core as a simple sp³-σ core. Diaminocylohexane is such an effective core for the systematic development of many kinds of isomers via geometric tuning as well as for reducing the self-aggregation tendency of PDIs. Depending on the anchoring position of the PDI units on the cyclohexane core (ortho-, meta- and para-), isomers exhibited differences in solubility and crystallinity. Among the studied isomers, ortho-substituted t-OCP was found to have a highly twisted molecular structure which minimizes the strong tendency towards crystallization due to individual PDI moieties. The unique geometrical nature of the t-OCP isomer led to the highest power conversion efficiency (PCE = 6.23%) of bulk heterojunction (BHJ) polymer solar cells (PSCs) with a higher short-circuit current density (J_sc) and fill factor (FF). It is mainly ascribed to the formation of a nanophase interpenetrating network with well-balanced carrier mobility in the blend film.