Chemical bath deposition of TiO 2 from TiCl 4 is an often used treatment that improves the photocurrent from dye-sensitized TiO 2 solar cells. In this paper, charge density and kinetic data are used to show that the main effects of this treatment are an 80 mV downward shift in the TiO 2 conduction band edge potential and a 20-fold decrease in the electron/electrolyte recombination rate constant. Together, these changes increase the quantum efficiency of charge separation at the interface, thus providing the observed increase in the photocurrent. The reduction in the recombination rate constant allows a greater concentration of electrons to accumulate at V oc , thus offsetting the V oc loss otherwise expected from the conduction band edge shift. Photocurrent transients and charge extraction data are used to show that the TiCl 4 treatment has little effect on the transport of electrons at short circuit. The electron/electrolyte recombination rate constant at short circuit has been measured with the CCTPV (Constant Current Transient PhotoVoltage) technique. The results further confirm that any improvements in transport could not cause the beneficial effect of the TiCl 4 treatment. Verification of the CCTPV technique is undertaken by comparison to transient absorption and by a model of the technique. Charge separation in dye-sensitized cells concerns two steps, charge injection and dye regeneration. Transient optical experiments to determine which process is improved by the TiCl 4 treatment are discussed.

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).

This paper presents an overview of the research carried out by a European consortium with the aim to develop and test new and improved ways to realise dye-sensitized solar cells (DSC) with enhanced efficiencies and stabilities. Several new areas have been explored in the field of new concepts and materials, fabrication protocols for TiO2 and scatterlayers, metal oxide blocking layers, strategies for co-sensitization and low temperature processes of platinum deposition. Fundamental understanding of the working principles has been gained by means of electrical and optical modelling and advanced characterization techniques. Cost analyses have been made to demonstrate the potential of DSC as a low cost thin film PV technology. The combined efforts have led to maximum non-certified power conversion efficiencies under full sunlight of 11% for areas < 0 center dot 2 cm(2) and 10 center dot 1% for a cell with an active area of 1 center dot 3 cm(2). Lifetime studies revealed negligible device degradation after 1000hrs of accelerated tests under thermal stress at 80 degrees C in the dark and visible light soaking at 60 degrees C. An outlook summarizing future directions in the research and large-scale production of DSC is presented