Synthesis, characterization and photovoltaic properties of two novel near-infrared absorbing perylene dyes containing benzo[e]indole for dye-sensitized solar cells

Two novel near-infrared absorbing perylene imide derivatives (I and II) with benzo[e]indole were designed and synthesized as sensitizers for dye-sensitized solar cells (DSSCs), and their structures were characterized by 1H NMR, 13C NMR, FT-IR, UV–vis, MS-ESI spectra, etc. The absorption spectra, electrochemical and photovoltatic properties of I and II were extensively investigated. Two perylene dyes have wide absorption bands with high molar extinction coefficients over the entire visible spectrum. Electrochemical properties indicated that the electron injection process from the excited dye molecule to TiO2 conduction band was energetically permitted. However, the preliminary photophysical and photoelectrochemical measurements show that the two perylene dyes have lower overall conversion efficiency on DSSCs application, although they have broad and intense absorption spectra in the visible region (up to 800 nm). This may be that the perylene imide group, which contains strong electron-withdrawing nature has effect on the polarity of the whole molecule, resulting in the unbeneficial transferring direction of photo-generated electrons, which decreases the overall photocurrent performance.