a 重庆科技学院 冶金与材料工程学院 重庆 401331;
b 重庆大学 化学化工学院 重庆 400030
Charge Recombination in Dye-sensitized Solar Cells with Low Adsorbed Concentration of Dye
Tang Xiaoa, Wang Yuxunb
a College of Metallurgy and Materials Engineering, Chongqing University of Science and Technology, Chongqing 401331;
b College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030
Photovoltaic conversion performances of dye-sensitized solar cells (DSCs) are significantly influenced by the interface charge recombination in DSCs. Lots of factors affecting the charge recombination, such as surface states of TiO2 and components of electrolytes, have been studied and dyes have been always ignored for the charge recombination in DSCs. Although the charge recombination occurring between the injection electrons and triiodide in electrolyte is calculated to take priority kinetically to the one between the injection electrons and oxidized dye molecules, dyes are not independent from the electrolyte related electron recombination. Instead by dye molecules themselves, the chance of injection electrons recaptured by triiodide in electrolyte could rise due to the increase of the adsorbed concentration of dye, which leads to the local concentration of triiodide increasing. In this paper, an effect of low charge recombination in DSCs with low adsorbed concentration of dye is observed. The adsorbed concentration of dye is defined as the adsorbed amount of dye in unit specific surface area of TiO2 films and adjusted by adsorbing similar amount of dye on the surface of TiO2 films with different film thickness. The influence of the adsorbed concentration of dye on the charge recombination in DSC is investigated by the electrochemical impedance spectroscopy (EIS) technology. It turns out that with the adsorbed concentration of dye decreasing, the electron lift time within TiO2 film and the interface resistance of TiO2/electrolyte increase significantly, which indicates the charge recombination in DSC decrease. Owing to this effect, with the TiO2 film thickness increasing from about 2 μm to 18 μm, the cells keep the fill factor (ff) as high as 0.72～0.80. And the energy conversion efficiency loss, which resulted from the increase of the active area of TiO2 photoanode from 0.25 cm2 to 1 cm2, decreased from 34.7% to 19.6%.