TECHNOLOGY FOCUS - POLYMERS - Preparation (claimed): 2-(5-Hexylthiophen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane is reacted with 3-bromothiophene under oxygen conditions in dark. Tetrakis(triphenylphosphine)palladium is added as catalyst and Suzuki reaction is carried out with toluene solution of potassium carbonate at 70-120 degrees C under reflux for 2-3 days, to obtain 2-hexyl-5-(thiophen-3-yl)thiophene. The obtained compound is dissolved in dichloromethane, added in 2 bottles, and treated under dark conditions. 2 eq N-bromosuccinimide is dissolved in N,N-dimethylformamide, dripped in the bottles, and reacted for 4-5 hours to obtain 2,5-dibromo-3-(5-hexylthiophen-2-yl)thiophene. The obtained compound is subjected to Suzuki coupling reaction with 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole in the presence of catalyst and potassium carbonate dissolved in tetrahydrofuran, at 70-75 degrees C for 2-3 days under reflux, to obtain polymer of formula (II). Or, polymer of formula (III) is obtained by the following method. 2-(5-Hexylthiophen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane is reacted with 3,4-dibromo-thiophene under oxygen conditions in dark. Tetrakis(triphenylphosphine)palladium is added as catalyst and Suzuki reaction is carried out with toluene solution of potassium carbonate at 70-120 degrees C under reflux for 2-3 days, to obtain 3,4-bis(5-hexylthiophen-2-yl)thiophene. The obtained compound is dissolved in dichloromethane, added in 2 bottles, and treated under dark conditions. 2 eq N-bromosuccinimide is dissolved in N,N-dimethylformamide, dripped in the bottles, and reacted for 4-5 hours to obtain 2,5-dibromo-3,4-bis(5-hexylthiophen-2-yl)thiophene. The obtained compound is subjected to Suzuki coupling reaction with 4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,1,3-benzothiadiazole in the presence of catalyst and potassium carbonate dissolved in tetrahydrofuran, at 60-90 degrees C for 2-3 days under reflux, to obtain polymer of formula (III).