TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Claimed): Preparation (P1) of (I) involves: reacting at least one disubstituted naphthoheterodiazole compound of formula (II) with at least one monostannylated benzodithiophene compound of formula (III).X=halogen atom selected from chlorine, bromine or iodine;R8-R10=H, linear or branched 1-20C alkyl or optionally substituted cycloalkyl.Preferred Process: The compounds (II) and (III) are used in molar ratios of 1:2-1:4. The process (P1) is carried out in the presence of at least one catalyst containing palladium. The compound (II) and the catalyst containing palladium are used in molar ratios of 100:0.1-100:6. The compound (II) is used at a molar concentration of 0.005-1 M. The process (P1) is carried out in the presence of at least one non-anhydrous dipolar aprotic organic solvent. The process (P1) is carried out at 40-150 degrees C for 10 minutes to 10 hours. Preferred Components: The catalyst containing palladium is selected from compounds of palladium in oxidation state (0) or (II). The catalyst containing palladium is dichloro-(bis(triphenylphosphine))palladium(II) (Pd(PPh3)2Cl2). The non-anhydrous dipolar aprotic organic solvent is selected from non-anhydrous dimethylsulfoxide (DMSO), non-anhydrous N,N-dimethylformamide (DMF), non-anhydrous N,N-dimethylacetamide (DMAc) and/or non-anhydrous N-methylpyrrolidone (NMP). Preferred Definitions:    Z=S;    R1-R5=H;R6 and R7=n-butyl.    SPECIFIC COMPOUNDS - One compound is specifically claimed as (I), i.e., 4,9-bis(7',8'-dibutylbenzo(1',2'-b':4',3'-b'')dithien-5'-yl)naphtha (2,3-c)(1,2,5)thiadiazole (Ia).    EXAMPLE - A mixture of 10.7 g of tri-n-butyl(7,8-dibutylbenzo(1,2-b:4,3-b')dithien-5-yl)-stannane, 2.89 g of 4,9-dibromonaphtho-(2,3-c)(1,2,5)thiadiazole, 800 ml of non-anhydrous dimethylsulfoxide (DMSO) and 295 mg of dichloro(bis-(triphenylphosphine))palladium(II) (Pd(PPh3)2Cl2), was heated at 80 degrees C for 30 minutes. After work up, 4,9-bis(7',8'-dibutylbenzo(1',2'-b':4',3'-b'')dithien-5'-yl)naphtho-(2,3-c)-(1,2,5)thiadiazole (Ia) had been formed with 95% yield. About 6 g of polymethylmethacrylate (PMMA) and 183.8 mg of compound (Ia) were dissolved in 30 ml of 1,2-dichlorobenzene. The solution obtained was subsequently uniformly deposited on a sheet of PMMA (dimensions 300 mm x 90 mm x 6 mm). A transparent sheet (test) was obtained, having a purple color conferred to it by the film whose thickness proved to 50-100 mu m. A photovoltaic cell was then applied to one of the edges of the polymeric sheet (test). Similarly a comparative sheet was prepared without using 49.5 mg of 4,7-di(thien-2'-yl)-2,1,3-benzothiadiazole (DTB) instead of the compound (Ia). A photovoltaic cell was then applied to one of the edges of the polymeric sheet (comparative). The test and comparative sheets were illuminated with a light source having a power of 1000 W/m2, and the electric power generated by the illumination was measured. The average power generated by test/comparative sheets was 10.08/5.01 mW, respectively.