Electron donating polymer and organic solar cell including the same

A polymer, comprising:

• a repeating unit A represented by the following Chemical Formula 1;
• and
• a repeating unit B represented by the following Chemical Formula 2:
• wherein, in Chemical Formula 1,
• X1 is the same or different in each repeating unit, and is independently a group including at least two ester residual groups and a substituted or unsubstituted divalent aliphatic organic group linking the at least two ester residual groups, and
• X2 is the same or different in each repeating unit, and is independently one selected from hydrogen, a halogen, a substituted or unsubstituted C1 to C20 aliphatic organic group, a hydroxyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C1 to C20 ester group, a thiol group, and —SR100, wherein R100 is one selected from a substituted or unsubstituted C1 to C20 aliphatic organic group, a substituted or unsubstituted C2 to C30 aromatic organic group, and a substituted or unsubstituted C2 to C30 heterocycloalkyl group,
• wherein, in Chemical Formula 2,
• X3 and X4 are the same or different, and are each independently one selected from hydrogen, a halogen, a substituted or unsubstituted C1 to C20 aliphatic organic group, a hydroxyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C1 to C20 ester group, a thiol group, and —SR101, wherein R101 is a substituted or unsubstituted C1 to C20 aliphatic organic group, a substituted or unsubstituted C2 to C30 aromatic organic group, and a substituted or unsubstituted C2 to C30 heterocycloalkyl group,
• wherein the repeating unit A includes one selected from a repeating unit represented by the following Chemical Formula 5-1, a repeating unit represented by the following Chemical Formula 5-2, and a combination thereof:
• wherein, in Chemical Formulas 5-1 and 5-2,
• X2 is the same or different in each repeating unit, and is independently one selected from hydrogen, a halogen, and a substituted or unsubstituted C1 to C20 alkyl group,
• X5 to X7 are the same or different, and are each independently a substituted or unsubstituted divalent C1 to C10 aliphatic organic group, and
• R1 and R2 are the same or different, and are each independently one selected from hydrogen, and a substituted or unsubstituted C1 to C10 aliphatic organic group, and
• wherein, in Chemical Formula 2,
• X3 and X4 are the same or different, and are each independently one selected from hydrogen, a halogen, a substituted or unsubstituted C1 to C15 alkyl group, a substituted or unsubstituted C1 to C15 alkoxy group, and —SR102, wherein R102 is a substituted or unsubstituted C1 to C15 alkyl group.