NOVELTY - A thiophene group-containing compound (1a'), (1b') or (II') including structural unit (III-i) and excluding structural unit (III-ii) is new.    USE - New thiophene group-containing compound is used for polymer for composition for organic-semiconductor material for semiconductor film for organic thin-film solar cell (all claimed) and wet dye-sensitized solar cell.    ADVANTAGE - The thiophene group-containing compound provides organic thin-film solar cell having excellent prevention property of coating unevenness, heat resistance and durability.    DETAILED DESCRIPTION - A thiophene group-containing compound formula (1a'), (1b') or A-B'-C- B"-A? (II') including structural unit of formula (III-i) and excluding structural unit of formula (III-ii) is new.    X1=C(R2)2, N(R3), O, S or Si(R3)2;    X2=C(R2)2, N(R3), O or Si(R3)2;    X3=C(R2)2 or S;    X4=N(R3), O, S or Si(R3)2;    R1,R2=H, halo, alkyl, cycloalkyl, aryl or hetero aryl;    R3=H, alkyl, cycloalkyl, aryl or hetero aryl;    A,B',C',B",A'=cyclocondensed mono-cyclic rings, where A and A' are aromatic 5-membered rings of formula (a), B' and B" are aromatic 5-membered rings of formula (b), and C? is benzene ring or 6-membered heteroaromatic ring;    Xa,Xb=C(R2)2, O, N(R3), S or Si(R3)2;    X8=X2;    X9=X1;    R4=R1;and    Ya,Yb=halo, trifluoromethane sulfonyloxy, trialkyl tin, borate or boric acid.    INDEPENDENT CLAIMS are included for the following:    (1) composition, which contains polymer having structural unit of formula (Ia), (Ib) or (II') including structural unit of formula (II-i) and excluding structural unit of formula (II-ii), in organic solvent;    (2) semiconductor film, which has photoelectric conversion ability by carrying out coating formation using the composition; and    (3) organic thin-film solar cell (10), which has a primary electrode (11), a secondary electrode (12) and a photoelectric converting layer (3) arranged in between primary electrode and secondary electrode. The photoelectric converting layer contains the polymer.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of organic thin-film solar cell.    Photoelectric converting layer (3)    Organic thin-film solar cell (10)    Electrodes (11,12)    Hole transportation layer electrode (21)    Electron carrying layer (22)