NOVELTY - Conjugated polymer derivative (I) is new.    USE - Conjugated polymer derivative used in solar battery and polymer field-effect transistor (claimed).    ADVANTAGE - The conjugated polymer derivative ensures enhanced solubility.    DETAILED DESCRIPTION - Conjugated polymer derivative of formula (I) is new.    D=benzene, thiophene, naphthalene, anthracene, perylene, fluorene, triphenylamine, phenothiazine, pyrrole, pyrazine, thiazole, pyridine, biphenyl pyridine, quinoline, furan, biphenyl, porphyrin, thieno (3,2-b) thiophene, thieno (3,4-b) thiophene, thieno (2,3-b) thiophene, dithieno (3,2-b:2',3'-d) thiophene, carbazole, indole, 4,8-bis-alkoxylated oxacillin (1,2-b:4,5-b) dithiophene, benzo (l,2-b:4,5-b) dithiophene, benzo(1,2-b:4,5-b')bisthiophene-4,8-dione, benzo (b) naphtho (2,3-d) thiophene, naphtho (4,5-b:8,9-b') dithiophene, naphtho (3,4-b:7,8-b) dithiophene, benzo (1,2-b:4,5-b') dithiophene or thieno (3,2-b)thiophene-benzo (1,2-b:4,5-b);    R1 and R2=H, 1-20C alkyl, 1-20C alkoxy, 1-20C ester, sulfone, sulfoxide, aryl, aralkyl, haloalkyl, heteroalkyl or 2-20C alkenyl groups;    X=H, F, Cl, Br or I;    n=more than 4;    Y'=carbonyl group, sulfonyl, sulphoxide, furan, thiophene or selenophene; and    m=1-20.    INDEPENDENT CLAIMS are included for:    (1) a method for preparing conjugated polymer derivative (I);    (2) a method for preparing cyclic derivative (II), which involves mixing 4,6-dibromothieno (3,4-b) thiophene-2-carboxylic acid with polyethylene glycol monomethyl ether in presence of an organic solvent i.e. dichloromethane, adding catalyst dicyclohexyl carbodiimide and 4-dimethylaminopyridine at room temperature for 24 hours, and extracting obtain solution with ether, preferably petroleum ether through column chromatography to obtain desired product;    (3) a method for preparing 2-(2-(2-methoxyethoxy)ethoxy)ethyl 6-(8-(5-(2-ethylhexyl)thiophen-2-yl)-11-methyl-2-(5-(2-propylhexyl)thiophen-2-yl)-4,10-dithiatricyclo(7.3.0.0(3,7))dodeca-1(9),2,5,7,11-pentaen-5-yl)-4-methyl-1,5-dihydropentalene-2-carboxylate derivative of formula (III), which involves treating 2-(2-(2-methoxyethoxy)ethoxy)ethyl 4,6-dibromothieno(3,4-b)thiophene-2-carboxylate with (2-(5-(2-ethylhexyl)thiophen-2-yl)-8-(5-(2-propylhexyl)thiophen-2-yl)-11-(trimethylstannyl)-4,10-dithiatricyclo(7.3.0.0(3,7))dodeca-1,3(7),5,8,11-pentaen-5-yl)trimethylstannane in presence of toluene and palladium compound at 80-120 degrees C, preferably 90-110 degrees C for 24-48 hours to obtain desired product; and    (4) a method for preparing 2-(2-(methoxymethoxy)ethoxy)ethyl 4,6-dibromothieno(3,4-b)thiophene-2-carboxylate derivative, which involves treating 2-(2-(methoxymethoxy)ethoxy)ethan-1-ol with 4,6-dibromothieno(3,4-b)thiophene-2-carboxylic acid in presence of dicyclohexyl carbodiimide and dichloromethane with 4-dimethylaminopyridine at room temperature for 24 hours to obtain desired product.    A=dialkyl radical or ester radical;    B=Cl, Br or I; and    n=not defined.