Injection and Recombination in Dye-Sensitized Solar Cells with a Broadband Absorbance Metal-Free Sensitizer Based on Oligothienylvinylene

A new metal-free sensitizer for improved light harvesting with dye-sensitized solar cells (DSC) has been synthesized and fully characterized. The molecular sensitizer was engineered by linking the tiophenes groups by methine units, improving light absorption until 760 nm wavelength. In conventional DSC configuration the dye produces short-circuit current density of 13.4 mA/cm² at 1.5 AM illumination (100 mW cm⁻²) and the incident photon-to-current conversion efficiency (IPCE) of 58%. The causes for the limitation to the photocurrent are investigated by impedance spectroscopy measurements, and it is shown that metal-based and metal-free molecular sensitizers show distinct characteristics concerning the blocking of the TiO₂ surface with coadsorbents to prevent electron recombination.