TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): The thiophene-benzothiadiazole copolymer (I) is prepared by subjecting 7-bromo-4-(7-bromo-5-iodo-2,1,3-benzothiadiazol-4-yl)-5-iodo-2,1,3-benzothiadiazole and ethyne compound of formula R2-(CC)-R3 (ii) in molar ratio of 1:2 to cyclization reaction under protection of inert atmosphere in primary solvent in presence of primary catalyst and primary alkali solution at 10-50 degrees C for 2 hours, obtaining thiadiazole derivative of formula (iii), and subjecting thiadiazole derivative (iii) and thiophene derivative of formula (iv) in molar ratio of 1:1.5-1.5:1 to Suzuki coupling reaction in presence of secondary catalyst and secondary alkali solution in secondary solvent at 50-120 degrees C for 12-100 hours. Preferred Process: The 7-bromo-4-(7-bromo-5-iodo-2,1,3-benzothiadiazol-4-yl)-5-iodo-2,1,3-benzothiadiazole is prepared by 4-nitrobenzene-1,2-diamine to thionyl chloride, stirring, adding pyridine, carrying out reflux reaction at 85 degrees C, obtaining 5-nitro-2,1,3-benzothiadiazole, adding 5-nitro-2,1,3-benzothiadiazole to hydrobromic acid, carrying out reflux reaction at 127 degrees C for 30 minutes, dropping liquid bromine, continuously reflowing, obtaining 4,7-dibromo-5-nitro-2,1,3-benzothiadiazole, adding copper powder in presence of a catalyst in N,N-dimethyl formamide as solvent, heating to 120 degrees C for 3 hours, obtaining 7-bromo-4-(7-bromo-5-nitro-2,1,3-benzothiadiazol-4-yl)-5-nitro-2,1,3-benzothiadiazole, adding tin chloride in tetrahydrofuran solvent, heating to 100 degrees C, and refluxing for 10 hours. The thiophene derivative (iv) is prepared by adding 2,5-dibromothiophene of formula (v) in tetrahydrofuran solvent, then adding n-butyl lithium into solvent, adding 4,4,5,5-tetramethyl-2-(propan-2-yloxy)-1,3,2-dioxaborolane, and reacting. Preferred Composition: The primary catalyst is palladium acetate. The amount of primary catalyst is 10 mol% with respect to amount of 7-bromo-4-(7-bromo-5-iodo-2,1,3-benzothiadiazol-4-yl)-5-iodo-2,1,3-benzothiadiazole. The secondary catalyst is tetra (triphenyl phosphine) palladium. The amount of secondary catalyst is 0.05-20 mol% with respect to amount of thiophene derivative (iv). The primary alkali solution is tributylamine solution. The molar ratio of primary alkali solution and ethyne compound (ii) is 1:1. The secondary alkali solution is potassium tertbutoxide, sodium tert-butoxide, potassium carbonate and/or sodium carbonate aqueous solution. The amount of secondary alkali solution is 10 times of amount of thiophene derivative (iv). The primary solvent is N,N-dimethyl formamide. The secondary solvent is tetrahydrofuran, ethylene glycol dimethyl ether, benzene or toluene.