Characterization of the pore filling of solid state dye sensitized solar cells with photoinduced absorption spectroscopy

Abstract

Near steady-state photoinduced absorption (PIA) and UV-Vis absorption spectroscopy are used to characterize the pore filling of spiro-MeOTAD (2, 2′, 7, 7′ -tetrakis-(N, N -di- p -methoxyphenylamine) 9, 9′ -spirobifluorene) into the nanoparticulate TiO2 electrode of a solid-state dye-sensitized solar cell (ssDSC). The volumetric ratio of filled to unfilled pore volumes, as well as the optical signature of interacting chemical species, that is, the hole-transfer yield (HTY), are investigated. PIA spectroscopy is used to measure the HTY, relative to the amount of spiro-MeOTAD present, without needing to determine the extinction coefficients of the dye and spiro-MeOTAD cation species. The Beer-Lambert law is used to relate the relative PIA signal to the penetration length of the hole-conductor in the TiO2 film. For the sample thickness range of 1.4-5μm investigated here, the optimum characteristic penetration length is determined to be 3.1 + 0.46 μm, which is compared to 1.4μm for the 200mg mL-1 concentration of spiro-MeOTAD conventionally used. Therefore, doubling the effective penetration of spiro-MeOTAD is necessary to functionalize all the dye molecules in a ssDSC. © 2011 Carol Olson et al.