Substitution of ethylene with ethynylene in the photostable perylene-diimide-based dimers enables an elevated photovoltaic performance

Two excellent thermo-and photo-stability perylene diimide (PDI)-based dimers TVT-(PDI-HD)2 and TYT-(PDI-HD)2 possessing different twisting degree were prepared by choosing (E)-1,2-di(thien-2-yl)ethene (TVT) and 1,2-di(thien-2-yl)ethyne (TYT) as the central linking cores, and two N,N-bis(2-hexyldecyl)perylene-3,4,9,10-tetra-carboxylic acid diimide (PDI-HD) subunits as bilateral wings. Absorption spectra exhibited that TYT-(PDI-HD)2 possessed better complementarity with PTB7-Th than that of TVT-(PDI-HD)2. Density functional theory (DFT) calculation revealed that the dihedral angle between two PDI moieties was remarkably reduced from 87.30 degrees to 11.73 degrees and the exciton binding energy (Eb) was lowered from 0.396 eV to 0.367 eV when model molecule TVT-(PDI-B)2 was replaced with TYT-(PDI-B)2. As a consequence, after substituting ethylene with ethynylene in the PDI-based dimers, the PCE was significantly boosted from 1.27% to 3.47%, the observed 1.73-fold increase in PCE was mainly attributed to 107.26% increased JSC and 57.70% elevated FF resulting from improved absorp-tion, enhanced exciton dissociation efficiency, ameliorated electron mobility and desired microstructural morphology. These results demonstrated that tuning the linking core in PDI-based dimers can effectively boost the device efficiency in non-fullerene solar cells.