NOVELTY - Electron-donating polymers comprising a repeating unit (A) with thieno(3,4-b)thiophene repeating unit (III), 1,6-dithia-dicyclopenta(b,g)naphthalene repeating unit (I) and/or 1,7-dithia-dicyclopenta(b,i)anthracene repeating unit (II), and a repeating unit B with a benzo(1,2-b;4,5-b')dithiophene repeating unit (IV) and 1,6-dithia-dicyclopenta(b,g)naphthalene repeating unit (V), are new.    USE - The electron-donating polymers are useful in an organic solar cell (claimed).    ADVANTAGE - The electron-donating polymers: are capable of absorbing light with a wider wavelength region; and exhibit improved hole mobility and solubility in an organic solvent. The electron-donating polymers provide organic solar cell with improved photoelectric conversion efficiency, high short circuit current density than conventional organic solar cell, and improved hole mobility.    DETAILED DESCRIPTION - Electron-donating polymers comprising a repeating unit (A) with thieno(3,4-b)thiophene repeating unit of formula (III), 1,6-dithia-dicyclopenta(b,g)naphthalene repeating unit of formula (I) and/or 1,7-dithia-dicyclopenta(b,i)anthracene repeating unit of formula (II), and a repeating unit B with a benzo(1,2-b;4,5-b')dithiophene repeating unit of formula (IV) and 1,6-dithia-dicyclopenta(b,g)naphthalene repeating unit of formula (V), are new.    X1-X10 = 1-20C-aliphatic organic group, 1-20C-alkoxy, 1-20C-ester (all optionally substituted), H, halo, OH, thiol or SR100;    R100 = 1-20C-aliphatic organic group, 2-30C-aryl organic group or 2-30C-heterocycloalkyl (all optionally substituted);    R1-R4 = linear or branched 1-20C-alkyl, 3-20C-cycloalkyl, 1-20C-alkoxy, 6-30C-aryl, 2-30C-heteroaryl (all optionally substituted) or H (where optionally at least one of CH2 groups of R1-R4 is substituted by O, S, SO2, CO, OCO, COO, CH=CH, CC or SiR101R102);    R101, R102 = linear or branched 1-20C-alkyl, 3-20C-cycloalkyl, 1-20C-alkoxy, 6-30C-aryl, 2-30C-heteroaryl (all optionally substituted) or H;    X11, X12 = 1-20C-aliphatic organic group, 1-20C-alkoxy, 1-20C-ester (all optionally substituted), H, halo, OH, thiol or SR103;    R103 = 1-20C-aliphatic organic group, 2-30C-aryl organic group or 2-30C heterocycloalkyl (all optionally substituted);    X13, X14 = 1-20C-aliphatic organic group, 1-20C-alkoxy, 1-20 ester (all optionally substituted), H, halo, OH, thiol or SR104;    R104 = 1-20C-aliphatic organic group, 2-30C-aryl organic group or 2-30C-heterocycloalkyl group (all optionally substituted);    R5, R6 = linear or branched 1-20C-alkyl, 3-20C-cycloalkyl, 1-20C-alkoxy, 6-30C-aryl, 2-30C-heteroaryl (where optionally at least one of CH2 is substituted by O, S, SO2, CO, OCO, COO, CH=CH, CC or SiR105R106) or H;    R105, R106 = linear or branched 1-20C-alkyl, 3-20C-cycloalkyl, 1-20C-alkoxy, 6-30C-aryl, 2-30C-heteroaryl (all optionally substituted) or H;    X15, X16 = 1-20C-aliphatic organic group, 1-20C-alkoxy, 1-20C-ester (all optionally substituted), H, halo, OH, thiol or SR107; and    R107 = 1-20C-aliphatic organic group, 2-30C-aromatic organic group or 2-30C-heterocycloalkyl (all optionally substituted).    An INDEPENDENT CLAIM is included for an organic solar cell comprising an anode and a cathode configured to face each other; and a photoactive layer between the anode and the cathode, where the layer comprises an electron donor comprising the electron-donating polymer and an electron acceptor.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of the organic solar cell.    Organic solar cell (100)    Substrate (10)    Lower electrode (20)    Photoactive layer (30)    Upper electrode. (40)