TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Compound: The conjugated system polymer further contains benzothiadiazole-group-containing repeating unit of formula (2).R13-R26=R1-R10;R27,R28=H or alkyl;andn=1-1000.Preferred Component: The electron-donating organic material contains photovoltaic-element material containing electron-accepting organic material (6). The electron-accepting organic material is fullerene compound. The electron-donating organic material is arranged between an anode (2) and a cathode (4), to form a photovoltaic element. Preferred Definitions:    R1-R12=alkyl;and    R13-R28=alkyl.    EXAMPLE - 2,1,3-Benzothiadiazole (in g) (4.3), bromine (10) and 48% hydrobromic acid (150 ml) were added, stirred at 120 degrees C for 3 hours, cooled to room temperature, the deposited solid was filtered, washed using water (1000) and acetone (100 ml), and dried at 60 degrees C, to obtain 4,7-dibromo-2,1,3-benzothiadiazole. 3-octylthiophene (10.53) was dissolved in dimethyl formamide (120 ml). Then, N-bromo succinimide (10.5) was added and stirred at room temperature in nitrogen atmosphere for 6 hours, to obtain a solution. Then, water (100) and n-hexane (100), were added and an organic layer was fractionated, washed using water (100 ml) and dried using magnesium sulfate, to obtain 2-bromo-3-octylthiophene. Then, the obtained 2-bromo-3-octylthiophene (15) was dissolved in diethyl ether (100 ml) and cooled to -100 degrees C. Then, 1.6M hexane solution of n-butyl-lithium (35 ml) and dimethyl formamide (6.2 ml), were added and heat-stirred at room temperature for 2 hours, to obtain a solution. Then, 1N aqueous solution of ammonium chloride (200 ml) and dichloromethane (100 ml), were added and an organic layer was fractionated, to obtain 3-octylthiophene-2-al (12.1). The obtained 3-octylthiophene-2-al (12.1), zinc powder (8.47), tetrahydrofuran (200 ml) and titanium tetrachloride (7.1 ml), were added, heated and refluxed in nitrogen atmosphere for 1 hour. The obtained solution was added to ice water (1000 ml) and dichloromethane (300 ml) and an organic layer was fractionated, to obtain thiophene-containing compound of formula (3) (7.47). The obtained thiophene-containing compound (7.47) was dissolved in dimethylformamide (100 ml) and n-bromo succinimide (3.5), and stirred for 4 hours. Then, water (100 ml), n-hexane (100 ml) and dichlorometane (100 ml) were added and an organic layer was fractionated, to obtain bromo-substituted thiophene-containing compound of formula (4) (6.32). The obtained bromo-substituted thiophene-containing compound (5.4) was dissolved in diethyl ether (70 ml) and ccoled to -100 degrees C. Then, 1.6M hexane solution of n-butyl-lithium (7.5 ml), 2-isopropoxy 4,4,5,5-tetramethyl-1,3,2-dioxa-borolan (1.7) were added and heated for 24 hours. Then, water (100 ml) and dichloromethane (100 ml) were added and an organic layer was fractionated, to obtain boron-substituted thiophene-containing compound of formula (5) (2.36). The obtained 4,7-dibromo-2,1,3-benzothiadiazole (0.511), the obtained boron-substituted thiophene-containing compound (2.36), dimethylformamide (40 ml), potassium phosphate (1.5), tetrabutyl ammonium bromide (0.23) and acetic-acid palladium (16 mg) were added and stirred at 120 degrees C for 5 hours. Then, water (100 ml) and dichloromethane (100 ml) were added and an organic layer was fractionated, to obtain benzothiadiazole-containing compound of formula (6) (0.85). The obtained benzothiadiazole-containing compound (5 mg) was added to chloroform (1 ml) and subjected to ultrasonic irradiation for 30 minutes, to obtain a reaction solution. Then, fullerene 60C, an anode and cathode were used, and photovoltaic element was formed. The obtained photovoltaic element had short-circuit-current density of 5.74 mA/cm2, open circuit voltage of 0.75 v, fill factor value of 0.33 and photoelectric conversion efficiency of 1.4%.