Ultrafast and fast charge separation processes in real dye-sensitized solar cells

The increasing global energy consumption and the simultaneous non-renewable resources depletion with their rising contamination levels, make the present energy scenario unsustainable. Among all the renewable energies, the sun's energy through its direct conversion into electricity is one of the best alternatives. In particular, since 1991 dye-sensitized solar cells (DSSCs) have attracted considerable interest from the scientific and commercial communities due to their promising characteristics as solar light converters. Nevertheless, even though there have been many efforts to increase the photoconversion efficiency through the photovoltaic parameters improvement using novel materials and device construction approaches, the efficiency and stability are still open challenges. On this regard, several approaches and techniques are being used to analyze the dependence of the overall efficiency on these parameters. In particular, the fast and ultrafast time-resolved spectroscopy techniques have provided advances towards unraveling the rate constants and quantum yields of the individual processes taking place in sensitized films in air as well as in complete DSSCs. Thus, the aim of this review is to discuss the main recent findings and the importance of the application of these techniques to understand why certain complete DSSC configurations have been more successful than others in terms of good sunlight conversion efficiencies, as well as to draw the basic guidelines on how to make further improvements in DSSCs. We firmly believe that new advances in this research area using ultrafast laser-based spectroscopy will not only help to discover fundamental and yet unknown information about these devices, but will also have impact on related topics like photocatalysis and photonics, supporting both technologies' development and contributing to the growth of the fundamental knowledge on interactions among photons, electrons and materials. (C) 2015 Elsevier Ireland Ltd. All rights reserved.