No abstract

Here, we present an optical probe to determine the pore-filling fraction of the hole-conductor 2,2-7,7-tetrakis-N,N-di-pmethoxyphenylamine-9,9-spirobifluorene (spiro-OMeTAD) into mesoporous photoanodes in solid-state dye-sensitized solar cells (ss-DSCs). Based on refractive index determination by the film's reflectance spectra, and using effective medium approximations, we can extract the volume fractions of the constituent materials and hence quantify pore-filling. This non-destructive method can be used with complete films and does not require detailed model assumptions.pore-filling fractions of up to 80% were estimated for optimized solid-state DSC photoanodes, which is higher than that previously estimated by indirect methods.Additionally, we have determined transport and recombination lifetimes as a function of the pore-filling fraction via photovoltage and photocurrent decay measurements. While extended electron lifetimes were observed with increasing pore-filling fractions, no trend was found in the transport kinetics. The data suggests that a pore-filling fraction of at least 60% is necessary to achieve optimized performance in ss-DSCs. This degree of pore-filling is even achieved in 5 µm thick mesoporous photoanodes. We can therefore conclude from this study that pore-filling is not a limiting factor in the fabrication of thick ss-DSCs.

We demonstrate the viability of large area processing for solid-state dye-sensitized solar cells. We fabricate mini-modules comprising two photoactive regions connected in series, of 8 cm2 total active area, using the technique of doctor blade coating to deposit the hole-transporter material. For the optimized protocol we lose only 25% of the power conversion efficiency when compared to standard test devices which are only 0.12 cm2. We estimate pore-filling fractions using reflectance spectroscopy, showing that device performance is linked to changes in the volume of the mesoporous TiO2 photoanode infiltrated with hole-transporter as deposition temperature is varied.