NOVELTY - A new high-molecular compound has structural unit (I).    USE - New high-molecular compound is used for composition for ink and for forming thin film (all claimed). Uses include but are not limited to solar cell, photosensor, liquid crystal display, electrophoresis display and organic electroluminescent display.    ADVANTAGE - The high-molecular compound provides thin film with excellent photoelectric conversion efficiency.    DETAILED DESCRIPTION - A new high-molecular compound has structural unit of formula (I).    Ar1,Ar2=trivalent heterocyclic group;    X1=-O-, -S-, -C(=O)-, -S(=O)-, -SO2-, -Si(R3)(R4)-, -N(R5)-, -B(R6)-, -P(R7)- or -P(=O)(R8)-;    R3-R8,R50=silyl, silyloxy, silyl thio or silylamino (all substituted), H, halo, alkyl, alkyloxy, alkylthio, aryl, aryloxy, arylthio, arylalkyl, arylalkyloxy, aryl alkylthio, acyl, acyloxy, amide, acid-imide, optionally substituted amino, monovalent heterocyclic group, heterocyclic oxy group, heterocyclic thio, aryl alkenyl, aryl alkynyl, carboxy, or cyano;    R51=6C or more alkyl, 6C or more alkyloxy, 6C or more alkylthio, 6C or more aryl, 6C or more aryloxy, 6C or more arylthio, 7C or more arylalkyl, 7C or more arylalkyloxy, 7C or more aryl alkylthio, 6C or more acyl, or 6C or more acyloxy;    or X1+Ar2=heterocyclic ring including Ar1;and    or C(R50)(R51)+Ar1=heterocyclic ring including Ar2.    INDEPENDENT CLAIMS are included for the following:    (1) thin film;    (2) composition, which contain high-molecular compound and electron-accepting compound;    (3) ink, which contains the composition and solvent;    (4) dithiophene compound of formula (VIII)-(X); and    (5) cyclic compound of formula (XI) or (XII).    R52-R65=R50;    W1-W4=H, halo, alkyl sulfonate group, aryl sulfonate group, arylalkyl sulfonate group, boric-acid-ester residue, sulfonium methyl group, phosphonium methyl group, phosphonate methyl group, monohalogenated methyl group, boronic-acid residue, formyl group, vinyl group, or organic tin residue;    V1,V2=H, alkali metal, alkyl, aryl, or arylalkyl;    Ar3-Ar6=trivalent heterocyclic group;and    Z=arylene group or bivalent heterocyclic group.