At present, one of the most studied molecular device for the conversion of sunlight into electricity is the dye-sensitised solar cell (DSSC). To date, ruthenium polypyridyl complexes have shown the highest light-to-energy conversion efficiencies because of their photophysical, photochemical and electrochemical properties. In addition, the overall efficiency achieved by DSSCs is strongly dependent on the interfacial charge-transfer reactions that take place between the different components of the solar cell: the injection of electrons into the conduction band of the semiconductor by the dye, the transport of electrons through the semiconductor towards the working electrode contact, dye regeneration by the redox pair present in the electrolyte and the recombination reaction between the photoinjected electrons in the semiconductor and the oxidised species of the dye and the electrolyte. This microreview comprises: (i) the operational principles of complete functional photovoltaic devices and (ii) several synthetic methods, properties and main applications of most relevant homoleptic and heteroleptic ruthenium complexes reported in the literature.