Evaluation of Limiting Factors Affecting Photovoltaic Performance of Low-Temperature-Processed TiO_2 Films in Dye-Sensitized Solar Cells

摘要

Limiting factors affecting photovoltaic performance of dye-sensitized solar cell employing low-temperature-processed TiO_2 films were investigated. TiO_2 films were prepared at a low temperature of 2008C using the normal alcohol-containing binderfree TiO_2 paste (LT200). Their photovoltaic performance was compared to a high-temperature (550 ℃) annealed TiO_2 film prepared using a polymer binder containing TiO_2 paste (HT550). Compared to the proportional increase in conversion efficiency with TiO_2 film thickness upto 14 mm for HT550, the increase in efficiency was terminated at relatively smaller thickness of about 8 mm for LT200 mainly due to unaugmented photocurrent. From the transient photocurrent-voltage studies, the electron transport rate was found to be almost identical, while charge recombination was one order of magnitude faster for LT200. Consequently, the electron diffusion length was more than 2-3 times shorter for LT200 than for HT550. Electron diffusion length and electron life time obtained from electrochemical impedance analysis were well consistent with those observed from transient measurement. Density of states (DOS) was evaluated to be shallow and narrow in LT200, which was responsible for limiting photovoltaic performance in the low-temperature processed TiO_2 film.