染料敏化太阳能电池中低染料吸附浓度下的界面电荷复合效应

Charge Recombination in Dye-sensitized Solar Cells with Low Adsorbed Concentration of Dye

在保持染料吸附量不变的条件下,通过增加TiO2薄膜厚度来降低染料在TiO2薄膜表面的吸附浓度.研究了染料吸附浓度与染料敏化太阳能电池(DSC)中界面电荷复合效应的关系.研究发现,在低染料吸附浓度下,DSCs中界面电荷复合效应明显降低,并由此使得DSC在薄膜厚度增加时,仍能保持0.72～0.80的高填充因子;在TiO2光电极有效面积由0.25 cm2增大到1 cm2时,总光电转换效率(η)损失由34.7%减少到19.6%.

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 TiO2films and adjusted by adsorbing similar amount of dye on the surface of TiO2films 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 TiO2photoanode from 0.25 cm2to 1 cm2,decreased from 34.7% to 19.6%.