Control of solid-state dye-sensitized solar cell performance by block-copolymer-directed tio₂ synthesis

Hybrid dye-sensitized solar cells are typically composed of mesoporous titania (TiO₂), light-harvesting dyes, and organic molecular hole-transporters. Correctly matching the electronic properties of the materials is critical to ensure efficient device operation. In this study, TiO ₂ is synthesized in a welldefined morphological confinement that arises from the self-assembly of a diblock copolymer - poly(isoprene-b-ethylene oxide) (Pl-b-PEO). The crystallization environment, tuned by the inorganic (TiO₂ mass) to organic (polymer) ratio, is shown to be a decisive factor in determining the distribution of sub-bandgap electronic states and the associated electronic function in solid-state dye-sensitized solar cells. Interestingly, the tuning of the sub-bandgap states does not appear to strongly influence the charge transport and recombination in the devices. However, increasing the depth and breadth of the density of sub-bandgap states correlates well with an increase in photocurrent generation, suggesting that a high density of these sub-bandgap states is critical for efficient photo-induced electron transfer and charge separation.