Importance of 4-tert-Butylpyridine in Electrolyte for Dye-Sensitized Solar Cells Employing SnO2 Electrode

The photovoltaic performance of dye-sensitized solar cells (DSSCs) employing SnO2 electrodes was investigated while increasing the content of 4-tert-butylpyridine (TBP) in the conventional liquid-type electrolyte. As the added TBP content increased, the open circuit voltage (V-oc) and conversion efficiency were highly enhanced while the short circuit current (J(sc)) was not much affected. With the electrolyte of 2.0 M TBP, the V-oc conversion efficiency were increased by 26 and 33%, respectively, compared with the conventional electrolyte (0.5 M TBP). The electrochemical impedance spectra revealed that the enhancement of V-oc from the negative shift of the SnO2 conduction band potential and the increase in resistance of electron recombination by 1 order of magnitude. It is noteworthy that the optimized concentration of TBP for the SnO2 electrode is greatly larger than that for the TiO2 electrode. This may be due to the much faster electron recombination rate and more positive conduction band potential of the SnO2 electrode. The SnO2 electrode modified with TiO2 shell showed only slightly enhanced performance due to the similar effects of shell layer and those of the TBP. In contrast to the SnO2, TiO2 electrodes did not show performance enhancement with the electrolyte of TBP concentration larger than 0.5 M. The impedance spectra of symmetric dummy cells employing Pt counter electrodes indicated that the catalytic effect of Pt was deteriorated, and the resistance of electrolyte diffusion was increased by the higher concentration of TBP. This brings up the need for development of a counter electrode that TBP is not easily adsorbed on, and alternative additives to TBP which are not highly viscous.