NOVELTY - A thiophene-containing electron-donating polymer comprising a repeating unit A including a dithiophene-containing repeating unit (I), and a thiophene-containing repeating unit(s) (II)-(IV), is new.    USE - A thiophene-containing electron-donating polymer used for an organic solar cell (claimed).    ADVANTAGE - The electron-donating polymers capable of absorbing light with a wide wavelength region and improving hole mobility. The organic solar cell is capable of increasing a light absorption rate, a short circuit current density, an open circuit voltage, and/or hole mobility, and have improved efficiency.    DETAILED DESCRIPTION - A thiophene-containing electron-donating polymer comprising a repeating unit A including a dithiophene-containing repeating unit of formula (I), and a thiophene-containing repeating unit(s) of formulae (II)-(IV), is new.    X1, X2=H, halo, optionally substituted 1-20C aliphatic organic group, OH, optionally substituted 1-20C alkoxy group, optionally substituted 1-20C ester group, thiol group, or SR100;    R1, R2=H, optionally substituted 1-20C linear or branched alkyl group, optionally substituted 3-20C cycloalkyl group, optionally substituted 1-20C alkoxy group, optionally substituted 6-30C aryl group, and/or optionally substituted 2-30C heteroaryl group, where CH2 group(s) included in R1 and R2 is substituted with -O-, -S-, -SO2-, -CO-, -OCO-,-COO-, -CH=CH-, -C=C=C-, or -SiR101R102;    Z1-Z6=H, or electron withdrawing group;    n1, n2+n3, n4+n5+n6=1-5;    R4, R6, R7, and R9-R11=H, optionally substituted 1-20C linear or branched alkyl group, optionally substituted 3-20C cycloalkyl group, optionally substituted 1-20C alkoxy group, optionally substituted 6-30C aryl group, and/or optionally substituted 2-30C heteroaryl group, where CH2 group(s) included in R1 and R2 is substituted with -O-, -S-, -SO2-, -CO-, -OCO-,-COO-, -CH=CH-, -C=C=C-, or -SiR103R104;    R101, R102, R103,R104=H, optionally substituted 1-20C linear or branched alkyl group, optionally substituted 3-20C cycloalkyl group, optionally substituted 1-20C alkoxy group, optionally substituted 6-30C aryl group, and/or optionally substituted 2-30C heteroaryl group;    R3, R5, R8=H, halo, optionally substituted 1-20C aliphatic organic group, OH, optionally substituted 1-20C alkoxy group, optionally substituted 1-20C ester group, thiol group, or SR105;    R100, R105=optionally substituted 1-20C aliphatic organic group, optionally substituted 2-30C aromatic organic group, or optionally substituted 2-30C heterocycloalkyl group;    m4=0-5;    m6, m9, n2, n4=0-3;    m7, m11, n3, n6=0-4; and    m10, n5=0-2.    An INDEPENDENT CLAIM is included for an organic solar cell (100), comprising:    (A) an anode (20);    (B) a cathode (40); and    (C) a photoactive layer (30) between the anode and the cathode, the photoactive layer including an electron donor and an electron acceptor.    DESCRIPTION OF DRAWING(S) - The drawing is a cross-sectional diagram of the organic solar cell.    Substrate (10)    Anode (20)    Photoactive layer (30)    Cathode (40)    Organic solar cell (100)