TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: Thiophene compound of formula (IV) is reacted with n-butyl lithium and trimethyl tin chloride, and nucleophilic substitution reaction is carried out, to obtain trimethyl tin-containing compound of formula (V). Tin-containing compound (V) is reacted with 2-bromophenyl methyl sulfinyl acid catalyst and solvent, and Stille coupling reaction is carried out under inert and anaerobic condition, to obtain phenyl methyl sulfoxide compound of formula (VI). Phenyl methyl sulfoxide compound (VI) and trifluoromethane sulfonic acid are added and stirred in presence of phosphorus pentoxide as catalyst at room temperature and intramolecular ring-closing condensation reaction is carried out for 12-15 hours, to obtain benzothiophene compound of formula (VII). The benzothiophene compound (VII) is brominated, to obtain bromine-containing compound (A). Tin-containing thiophene compound of formula (VIII) is reacted with 4,7-dibromo-5-fluorobenzo(c)-1,2,5-thiadiazole in dry tetrahydrofuran, in presence of nitrogen gas, residual oxygen is removed, and catalyst is added rapidly at 60 degrees C. The resulting mixture is refluxed for 24 hours, to obtain thiadiazole compound of formula (IX). Thiadiazole compound (IX) is added to anhydrous tetrahydrofuran, cooled to -78 degrees C, n-hexane solution of n-butyl lithium is added, stirred at 78 degrees C or more for 2 hours, and trimethyl chloride is added, to obtain tin-containing compound (B). Preferred Composition The molar ratio of compound (A) and compound (B) is 1:1-1:1.5. The catalyst is bis (triphenylphosphine)palladium dichloride, tris (dibenzylideneacetone) dipalladium, or tris (2-methylphenyl)phosphine, or a mixture of tris(2-tolylphosphine) and tetrakis(triphenylphosphine)palladium. The addition amount of catalyst is 0.01-5 mol%. The molar ratio of Phenyl methyl sulfoxide compound (VI) and phosphorus pentoxide is 3-2.5:1. The molar ratio of tin-containing thiophene compound (VIII) and 4,7-dibromo-5-fluorobenzo(c)-1,2,5-thiadiazole is 2:1.    TECHNOLOGY FOCUS - POLYMERS - Preparation (claimed): Bromine-containing compound (A) of formula (II) and tin-containing compound (B) of formula (III) are added to organic solvent, dissolved under inert gas condition, and catalyst is added to the organic solvent, to obtain mixed solution. The mixed solution is subjected to Stille-coupling reaction at 60-120 degrees C for 24-72 hours, to obtain benzothiadiazole copolymer (I). Preferred Definitions:    n=20-30.