Effect of the adsorbed concentration of dye on charge recombination in dye-sensitized solar cells

Charge recombination is the most important factor limiting the power conversion efficiency of dye-sensitized solar cells (DSCs). Lots of factors affecting the charge recombination in DSCs have been investigated except the adsorbed concentration of dye on the surface of TiO2 film. By electrochemical impedance spectroscopy (EIS) analysis, it is found that with the adsorbed concentration of dye decreasing, both charge transport resistance at the TiO2/electrolyte interface and electron life time within the TiO2 photoanode increase, which indicates that the charge recombination in DSC decreases. Owing to this effect, the DSC keeps the fill factor as high as 0.75–0.78 even though the TiO2 film thickness exceeds 20 μm.

Graphical abstractWith the adsorbed concentration of dye decreasing, the increase of the charge transport resistance at the TiO2/electrolyte interface, as the radius of the semicircle was bigger and bigger, indicated that the charge recombination between the injected electrons transported within the TiO2 film and I3- in electrolyte decreased. As a result, the electron life time within the TiO2 photoelectrode (τr) increased, which was calculated from the decreased characteristic frequency (fmax).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Effect of the adsorbed concentration of dye on charge recombination in DSC was found. ► Charge recombination in DSC decreased with the adsorbed concentration of dye decreasing. ► Decrease of the adsorbed concentration of dye made the DSC keep high fill factor.