NOVELTY - A dye sensitized solar cell has a transparent conductive electrode substrate layer, a working electrode layer containing a porous film made of oxide semiconductor fine particles, a photo-sensitizing dye layer formed on a surface of the working electrode, a counter electrode layer, and an electrolyte layer containing substituted 4,5-dihydro-1H-pyrazole compound (I or II).    USE - Dye sensitized solar cell.    ADVANTAGE - The dye sensitized solar cell has better photovoltaic performance.    DETAILED DESCRIPTION - A dye sensitized solar cell has a transparent conductive electrode substrate layer, a working electrode layer containing a porous film made of oxide semiconductor fine particles, a photo-sensitizing dye layer formed on a surface of the working electrode, a counter electrode layer, and an electrolyte layer containing substituted 4,5-dihydro-1H-pyrazole compound of formula (I or II).    G=(-N(R2)-N.-) or (-N+(R2)=NA-);    n=2-5;    X,X1=1-20C alkyl, 2-16C alkenyl, 6-18C aryl, 7-18C aralkyl, 8-18C aralkenyl (all optionally substituted by halo, OR4, SR4, NR4R5, C(O)R4, C(O)OR4, O-C(O)-R4, C(O)NR4R5, NR4-C(O)-R5, NR4-C(O)-R5 or OC(O)NR4R5) or H, where aryl is additionally substituted by 1-16C aIkyl, 2-16C alkenyl or perfluorinated 1-16C alkyl, and alkyl and alkenyl are additionally interrupted by O, S or NR4;    X+X1=(=O), =S or =NR4;    Y1=1-16C alkylene, 1-16C alkenylene, 1-16C alkylene-6-18C-arylene-1-16C alkylene, 6-18C arylene (all optionally substituted by halo, OR4, SR4, NR4R5, C(O)R4, C(O)OR4, O-C(O)-R4, C(O)NR4R5, NR4-C(O)-R5, NR4-C(O)-R5 or OC(O)NR4R5) or direct bond, where arylene is additionally substituted by 1-16C alkyl, 2-16C alkenyl, perfluorinated 1-16C alkyl, and alkylene and alkenylene are additionally interrupted by O, S, NR4, C(O), C(O)O, O-C(O), C(O)NR4, NR4-C(O), NR4-C(O)-O, OC(O)NR4;    A-=anion of organic or inorganic acid, preferably anion of HPF6, HClO4, HBF4, HO3SCF3, HN(C2F5SO2)2, HC(CF3SO2)3, HC(C2F5SO2)3, HB(C2O4)2, HB(C6H5)4, HB(C6F5)4, HSbF6, HAsF6, HBr, HBF3C2F5, HPF3(CF2CF3)3, HCl, HI, CF3COOH or CH3COOH;    R1-R3=1-20C alkyl, 2-20C alkenyl, 3-20C cycloalkyl, 4-20C cycloalkenyl, 6-26C aryl, 7-30C aralkyl, 8-30C aralkenyl, 3-20C heteroaryl, 3-20C heteroaryl-1-20C alkyl, 3-20C heteroaryl-2-20C alkenyl or ferrocenyl (all optionally substituted by halo, OR4, SR4, NR4R5, C(O)R4, C(O)OR4, O-C(O)-R4, C(O)NR4R5, NR4-C(O)-R5, NR4-C(O)-R5 or OC(O)NR4R5), H or halo, where aryl and heteroaryl are additionally substituted by 1-15C alkyl, 2-16C aIkenyl, perfluorinated 1-16C alkyl, and alkyl, alkenyl, cycloalkyl and cycloalkenyl are additionally interrupted by O, S or NR4;    R4,R5=1-20C alkyl, 2-20C alkenyl, 3-20C cycloalkyl, 4-20C cycloalkenyl, 5-18C aryl, 6-30C aralkyl, 3-30C aralkenyl, 3-20C heteroaryl, 3-20C heteroaryl-1-20C alkyl, 3-20C heteroaryl-2-20C alkenyl;and    NR4R5=optionally substituted 5-, 6- or 7-membered heterocyclic ring.    INDEPENDENT CLAIMS are also included for the following:    (1) a substituted 4,5-dihydro-1H-pyrazole compound (I or II) with provisos, where X is not hydrogen and the compound (I or II) excludes salt of 6-oxo-1,3,5-triphenyl-5,6-dihydro-(1,2,4,5)tetrazin-1-ium tetrafluoro borate, salt of 1,5-dimethyl-6-oxo-3-phenyl-5,6-dihydro-(1,2,4,5)tetrazin-1-ium tetrafluoro borate, salt of 1,5-diisopropyl-6-oxo-3-phenyl-5,6-dihydro-(1,2,4,5)tetrazin-1-ium tetrafluoro borate, salt of 1,5-diisopropyl-6-oxo-3-pyridin-2-yl-5,6-dihydro-(1,2,4,5)tetrazin-1-ium tetrafluoro borate, salt of 3-(1H-imidazol-2-yl)-1,5-diisopropyl-6-oxo-5,6-dihydro-(1,2,4,5)tetrazin-1-ium tetrafluoro borate and salt of 1,5-diisopropyl-3-(1-methyl-1H-imidazol-2-yl)-6-oxo-5,6-dihydro-(1,2,4,5)tetrazin-1-ium tetrafluoro borate, preferably salt of 1,5-dimethyl-6-oxo-3-phenyl-5,6-dihydro-(1,2,4,5)tetrazin-1-ium tetrafluoro borate and salt of 1,5-diisopropyl-6-oxo-3-phenyl-5,6-dihydro-(1,2,4,5)tetrazin-1-ium tetrafluoro borate    (2) an use of compound (I or II) as a redox pair in electrolyte of a dye sensitized solar cell.