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

Abstract

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-tetracarboxylic 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° to 11.73° 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 absorption, 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.