Ruthenium complex dyes and photovoltaic cells utilizing them as photosensitizers

A compound of formula (I): (X)nRuLL1 where n is 1 or 2, preferably 2, and in which Ru is ruthenium; each X independently is selected from Cl, SCN, H2O, Br, I, CN and SeCN and L is a ligand of formulae (a) to (g) and L1 is selected from a ligand of formulae (a) to (c) where each R independently is selected from OH, hydrogen, C1-20alkyl, -ORa or -N(Ra)2 and each Ra independently is hydrogen or C1-4alkyl.