Toward rational design of metal-free organic dyes based on indolo[3,2-b] indole structure for dye-sensitized solar cells

Three organic dyes containing a nitrogen-bridged phenylenevinylene (NPV: indolo[3,2-b]indole) unit were syrithesized and applied in dye-sensitized solar cells, where NPV was employed as a donor itself or as a pi-spacer with the extra-donor diphenylamine. The photophysical, electrochemical and photovoltaic properties of the dyes were investigated. All dyes displayed broad absorption spectra and high molar extinction coefficient, resulting in high light harvesting efficiency. The results showed that the dye with two cyanoacrylic acid as the acceptors exhibited photovoltaic performance of 7.39% under standard global AM 1.5 solar condition, better than the other two with only one acceptor. These results indicate that the NPV-based organic dye is a promising candidate for efficient DSSCs.