Synthesis, characterization, and photovoltaic properties of diketopyrrolopyrrole-oligothiophene/fullerene dyads

Low-band-gap dyad molecules containing diketopyrrolopyrole (DPP) chromophore and hexathiophene were designed and synthesized in combination with C60 and C70 derivatives as the electron acceptors. The effect of alkyl side chains in the donor parts on film morphology, thermal properties, and optical properties were investigated by X-ray diffraction analysis, differential scanning calorimetry, UV–vis absorption spectroscopy, and fluorescence spectroscopy. The donor part with a shorter alkyl side chain showed better packing of the π-plane and an enhancement of absorption in the longer-wavelength region, which led to higher JSC of organic solar cells. The use of C70 as the electron acceptor led to stronger absorption in the visible region, resulting in improved external quantum efficiency and JSC compared with those of the C60 derivatives. The single-component solar cell of the dyad with the methyl side chains and C70 derivative showed the power conversion efficiency of 0.84% with a relatively high JSC of 4.4 mA cm−2 under AM 1.5 illumination (100 mW cm−2).