Fluorinated naphtho[1,2-c:5,6-c’]bis[1,2,5]thiadiazole-containing π-conjugated compound: synthesis, properties, and acceptor applications in organic solar cells

The incorporation of electron-accepting units into π-conjugated systems is well-established as a powerful approach to tune the physical properties and frontier orbital energy levels of molecules. To realize semiconductors with novel functions, naphtho[1,2-c:5,6-c’]bis[1,2,5]thiadiazole (NTz) has been utilized as an effective electron-accepting unit. To enhance the electron-accepting nature of NTz in this work, the synthesis of fluorinated naphthobisthiadiazole (FNTz) was accomplished by the sequential introduction of amino functional groups into 1,5-difluoronapthalene derivatives to form fluorinated tetraaminonapthalene derivatives, followed by the formation of thiadiazole rings. Organic solar cells based on our synthesized FNTz acceptor in combination with poly(3-hexylthiophene) (P3HT) as a donor exhibit a significant improvement of power conversion efficiency (PCE) compared to the corresponding nonfluorinated NTz-based cells, reaching a high PCE of up to 3.12%. Investigation of the blend-film properties and device physics unambiguously reveals that the blend films based on P3HT and the FNTz-based compound shows good film morphologies and thus efficient charge generation and transport characteristics. These results demonstrate the potential of FNTz for an electron-accepting unit in organic semiconductors