NOVELTY - Photosensitizing transition metal complexes (I) are new.    USE - (I) are useful in photovoltaic cell (claimed) such as solar cell.    ADVANTAGE - (I) are photochemically stable, and improve the efficiency, durability and stability of dye sensitized nanocrystalline solar cell.    DETAILED DESCRIPTION - Photosensitizing transition metal complexes of formula (MLY4X) (I) are new.    M = transition metal comprising Ru(II), Os(II), Fe(II), Re(I) or Tc(I);    L = polypyridine ligand of formula (a);    A1-A3 = anchoring group comprising -COOH, -COON(C4H9)4, -PO(OH)2, -PO(OR1)2, -CO(NHOH), 1-50C alkyl, 2-50C alkylamide or 7-50C aralkyl;    R1 = 1-30C alkyl;    X = ligand comprising NCS-, Cl-, Br-, I-, CN-, NCO-, H2O or pyridine (optionally substituted by vinyl, primary, secondary or tertiary amino, alkylthio, arylthio, OH or 1-30C alkyl);    Y4 = (2,2')bipyridinyl group of formula (IVb-1), (1,10)phenanthroline group of formula (IVb-2), 2-pyridin-2-yl-quinoline group of formula (IVb-3), 1,2-dimethoxy-benzene, phthalic acid dimethyl ester or 2-methoxy-benzoic acid methyl ester (all substituted with R14), quinoxaline-2,3-dithiolate (substituted with R12), benzene-1,2-dithiolate (substituted with R12), CH(S-)2-N(R12)2, C(S-)2=N(R12)2, CH3-O-C(=O)-C(=O)-O-CH3, CH3-O-CH(R14)-CH(R15)-O-CH3, CH3-O-C(=O)-CH2-C(=O)-O-CH3, CH3-O-N(R14)-C(R15)=O-CH3, (1-(2-methoxy-phenyl)-meth-(E)-ylidene)-phenyl-amine, H2N-CH(R16)-CH(R17)-NH2 or R16-NH-(CH2)2-NH-R17; and    R10-R17 = 1-20C alkyl, 2-12C alkoxyalkyl, 2-12C perfluoroalkyl, 2-12C alkylamide, 1-12C aminoalkyl, 2-6C alkoxycarbonyl, 1-6C alkoxy, 6-12C aryl, CN, OH, nitro, amino, trifluoroalkyl group, halo or H.    An INDEPENDENT CLAIM is included for a photovoltaic cell comprising a support (8), a conductive layer formed on the support, and a porous semiconductor layer formed on the conductive layer, a counter electrode, and an electrolyte deposited between them, where the porous semiconductor layer carries (I).    DESCRIPTION OF DRAWING(S) - The figure shows a diagrammatic sectional view showing the structure of solar cell.    Substrate (1)    Electroconductive film (3) Porous photovoltaic layer (2)    Hole transporting layer (4)    Support. (8)