Properties of chromophores determining recombination at the TiO2-dye-electrolyte interface

Different classes of chromophores have been developed for the dye solar cell (DSC), including as the two main classes organometallic dyes, with Ru-based complexes and Zn-porphyrin complexes, and metal-free dyes. They result in different recombination behavior by electron transfer at the titania/dye/electrolyte interface, where the dye molecule plays a pivotal role. We present an overview of the main factors that control recombination depending on dye structural and electronic properties: the substituent's nature, the size and nature of the π bridge, the type of absorption onto the titania surface, and the structure of the donor electron moiety or anchoring group. Different recombination mechanisms arise, including direct recombination to redox electrolytes and through a dye cation intermediate.