In this study, the influence of the TiCl(4) post-treatment on nanocrystalline TiO(2) films as electrodes in dye-sensitized solar cells is investigated and compared to nontreated films. As a result of this post-treatment cell efficiencies are improved, due to higher photocurrents. On a microscopic scale TiO(2) particle growth on the order of 1 nm is observed. Despite a corresponding decrease of BET surface area, more dye is adsorbed onto the oxide surface. Although it seems trivial to match this finding with the improved photocurrent, this performance improvement cannot be attributed to higher dye adsorption only. This follows from comparison between incident photon to current conversion efficiency (IPCE) and light absorption characteristics. Since the charge transport properties of the TiO(2) films are already more than sufficient without treatment, the increase in short circuit current density J(SC) cannot be related to improvements in charge transport either. Transient photocurrent measurements indicate a shift in the conduction band edge of the TiO(2) upon TiCl(4) treatment. It is concluded that the main contribution to enhanced current originates from this shift in conduction band edge, resulting in improved charge injection into the TiO(2).

Flat structures consisting of dense dye-sensitized TiO 2 films with various materials for dye regeneration (TiO 2 /dye/regeneration material) are compared. Au and PEDOT:PSS were tested as metal or metal-like regeneration materials and compared with reference compounds, such as the redox couple I À /I 3 À in solution and p-typeCuSCN. Under the exclusion of TiO 2 bandgap excitation, the short-circuit photocurrent densities for the various structures differ by less than $ 30%, suggesting comparable charge separation efficiencies. The good performance of a metallic regeneration material implies, that the frequently assumed requirement of p-type or 'hole conducting' properties for the regeneration material in solid state dye solar cells is questionable.

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