Abstract

Two narrow band-gap small molecules with D(A-Ar)2 framework, namely DMPh(DPP-Py)2 and DFPh(DPP-Py)2, were designed and synthesized for high-performance small molecule organic solar cells (SMOSC), in which the 1,4-dimethoxybenzene (DMPh) and 1,4-difluorobenzene (DFPh) were employed as rigid donor cores, respectively, and the pyrenere (Py) unit is selected as terminal-capping groups on an electron-deficient diketopyrrolopyrrole (DPP)-based linear backbone. The impacts of the fluorine-sulfur (F⋯S) atoms and oxygen-sulfur (O⋯S) atoms noncovalent interaction on their absorption spectra, molecular energy levels, morphological properties, hole mobilities and photovoltaic properties were investigated thoroughly. The fluorinated DFPh(DPP-Py)2 possess a relatively lower-lying HOMO energy level, better miscibility of the blend with PC71BM, as well as higher mobility in comparison with those of the methoxyled DMPh(DPP-Py)2. As a consequence, the OSCs devices based on DMPh(DPP-Py)2 and DFPh(DPP-Py)2 exhibited PCEs of 5.47% and 7.54%, respectively. Obviously, the device based on DFPh(DPP-Py)2 presented a better performance, which should be ascribed to the improved simultaneously Voc of 0.77 V, Jsc of 15.3 mA cm−2, and FF of 64%. The results indicated that the choice of the fluorination designation on the molecular backbone is an effective approach to develop D(A-Ar)2 type small molecule donors for highly efficient solar cell applications.

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