Porphyrin Based Dye Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have emerged as an innovative solar energy conversion technology which provides a pathway for the development of cheap, renewable and environmentally acceptable energy production (Gledhill, Scott et al., 2005; O'Regan & Grätzel, 1991; Shaheen, Ginley et al., 2005). A typical DSSC consists of a sensitizing dye chemically anchored to a nanocrystalline wide band gap semiconductor, such as TiO2, ZnO or SnO2. The oxide structure is mesoporous in order to produce a high surface area for dye coverage, allowing the adsorbed monolayer to capture the majority of the incident solar flux within the dye band gap. The porous photoanode is immersed in an electrolyte which contains a redox mediator to transport positive charge to the counter electrode and maintain net electrical neutrality (Figure 1). Efficient charge separation is achieved through photoinduced electron injection from the excited state of the sensitizing dye into the conduction band of the metal oxide semiconductor. The resulting dye cations are subsequently reduced by the redox electrolyte, which also conducts the holes to the platinum-coated cathode. The solar to electric power conversion efficiencies of DSSCs depend on a delicate balance of the kinetics for injection, dye regeneration and recombination reactions (Haque, Palomares et al., 2005), with the best devices, currently based on ruthenium polypyridyl sensitizers and an iodide/triiodide redox mediator, exhibiting certified power conversion efficiencies of over 11% (Chiba, Islam et al., 2006).