Photoanode Area Dependent Efficiency and Recombination Effects in Dye-Sensitized Solar Cells

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Abstract
Efficiency and electron lifetimes in dye-sensitized solar cells (DSCs) fabricated from P25 titania nanoparticles were found to be strongly dependent on the photoanode area. Tin oxide nanowires, which already exhibit higher electron lifetimes than titania nanoparticles, also showed similar behavior. Most importantly, DSCs fabricated from these materials exhibited a non-uniform photovoltage profile laterally across photoanode for areas as large as 1 cm2. The non-uniformity in photopotential distribution is enhanced with a reduction in the photoanode area indicating edge effects at smaller areas. Dye desorption from the edges of the photoanode into the liquid electrolyte results in these edge effects and can play an important role in characterizing the DSC performance. Interestingly, DSCs made using anatase nanoparticles exhibiting strong dye adsorption showed a uniform photopotential along the lateral dimension of the photoanode. Further, P25 nanoparticles based DSCs showed no spatial photopotential variation when infiltrated with a solid state electrolyte indicating that dye desorption from the nanoparticle or nanowire surfaces is a crucial factor contributing to edge effects. Mapping the photopotential distribution is a valuable tool to understand and characterize edge effects in DSCs.

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