NOVELTY - Use of rylene derivative (I) or its mixtures as a photosensitizer in solar cells.    USE - (I) is useful as a photosensitizer in a dye sensitized solar cell (claimed).    ADVANTAGE - (I) exhibits strong light absorption and provides high stability to the solar cells. (I) exhibits reduced cell resistance.    DETAILED DESCRIPTION - Use of rylene derivative of formula (I) or its mixtures as a photosensitizer in solar cells.    X+carbonyl compounds = a six membered ring (where both the residue is -COOM); either    Y1 = e.g. -L-NR1R2 or H; or    Y1+amide compounds+H = six membered ring;    R = optionally substituted (het)aryloxy or (het)arylthio, whose 5-7 membered ring is interrupted by e.g. -O-, -S-, -CO-, -SO and/or -SO2-, and can be annealed;    P1 = an amino group; either    R1, R2 = 1-30C alkyl, 3-8C cycloalkyl or (het)aryl (all optionally substituted); or    NR1R2 = 5-7 membered ring;    B1 = 1-6C alkylene, phenylene or a combination of bridge members;    A = -COOM, -SO3M or -PO3M2;    M = e.g. H, monovalent or bivalent metal cation or ammonium salt of cyclic amine;    Ra = H, 1-30C alkyl, aryl or hetaryl; either    n = 0, 2 or 4 (when m is 0 or 1) or 0, 4 or 6 (when m is 2); and    p = 0, 2 or 4 (when m is 0); or    n+p = 0, 2 or 4; and    m = 0-2.    Full Definitions are given in the DEFINITIONS (Full Definitions) Field.    INDEPENDENT CLAIMS are included for:    (1) a dye sensitized photovoltaic cell containing (I) as a photosensitizer; and    (2) a rylene derivative of formula (Ia) or (I).    Ra = 1-30C alkyl, whose carbon chain is interrupted by -O-, -S- and/or -NR4-, -N=CR4-, -Ctriple bondC-, -CR4=CR4-, -CO-, -SO and/or -SO2-, and substituted by 1-12C alkoxy, 1-6C alkylthio, -NR9R10, (het)aryl and/or 4-7C cycloalkyl (whose carbon scaffold is substituted by -O-, -S- and/or -NR4), where the cycloalkyl- and (het)aryl are substituted by 1-18C alkyl and/or the substituents for alkyl residues, aryl or hetaryl, optionally saturated 5-7 membered ring, whose carbon scaffolding is interrupted by -O-, -S- and/or -NR4 and is annealed, where the total ring system is substituted by -NR9R10; and    X+-CO-N(-A-B1)-CO-+a carbonyl compound of formula (x3) = a six membered ring.    In formula (Ia): where n+p is 0 and one of the residue of Y1 is -L-NR1R2 or H, and at least one of the residue R1 or R2 is substituted by one of the aryl residue (c) in variable R, if L is a chemical bond.    In formula (I): if one of the residue of Y1 is -L-NR1R2 or -L-Z-R3 and the other is H, where at least one of the residue R1 or R2 in -L-NR1R2 is substituted by one of the aryl residue (c) in variable R, then L is a chemical bond.