Retardation of interfacial charge recombination by addition of quaternary ammonium cation and its application to low temperature processed dye-sensitized solar cells

Electron lifetime (tau) in dye-sensitized solar cells (DSC), using electrolytes containing I-/I-3(-) redox couple, was investigated with quaternary ammonium cations having various alkyl chain lengths, and it was found that the lifetime increased in the order tau(TPA) approximate to tau(TBA) < tau(THA) approximate to tau(THpA), where tau(TPA), tau(TBA), tau(THA) and tau(THpA) were the lifetimes with tetra-propyl, butyl, hexyl and heptyl ammonium cations respectively On the other hand, little influence of the cations oil electron diffusion coefficients was observed, indicating that the DSCs using these cations have longer electron diffusion length (L). New electrolyte compositions for DSCs were sought with THA(+) to increase the lifetime and L without compromising charge injection yield from the dye to TiO2 The electrolyte was applied for DSCs using TiO2 electrode prepared by 150 degrees C sintering. Under one-sun conditions (100 mW cm(-1)), newly prepared electrolytes showed at most 40% increase of energy conversion efficiency in comparison to conventional electrolytes and the highest value was 4.7%, which was the highest among the reported values of low temperature processed DSCs. The increase of the efficiency was achieved by higher short-circuit current induced by longer electron diffusion length and higher open-circuit voltage due to higher electron density.