TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The copolymer further comprises dioxopyrrole fused ring backbone-containing repeating unit of formulae (IV) and (V).A1,A2=16 group element.    TECHNOLOGY FOCUS - POLYMERS - Preparation (disclosed): A dioxopyrrole fused ring-containing compound of formula (i), dithieno fused ring-containing compound of formula (ii) and dithieno fused ring-containing compound of formula (iii) are polymerized by coupling reaction in presence of a catalyst, to obtain copolymer.X,Y'=halo, alkyl stannyl, alkyl sulfo, aryl sulfo, arylalkyl sulfo, boric acid-ester residue, sulfonium methyl, phosphonium methyl, phosphonate methyl, monohalogenation methyl, boric acid residue, formyl group, silyl, alkenyl or alkynyl. EXAMPLE - 0.26 mmol 1,3-Dibromo-5-octyl-4H,5H,6H-thieno(3,4-c)pyrrole-4,6-dione, 0.2 mmol 1,1-dioctyl-3,4-bis(prop-1-en-2-ylsulfanyl)-1H-silole and 0.082 mmol 4,10-dimethyl-7,7-bis(2-methylhexyl)-3,11-dithia-7-silatricyclo(6.3.0.02,6)undeca-1(8),2(6),4,9-tetraene were added into 50 mL two-opening round bottom flask as monomer under nitrogen atmosphere, and 3 mol% tetrakis(triphenylphosphine)palladium(0), 3 mol% triphenylphosphine containing heterogeneous palladium complex catalyst, 4.7 mL toluene and 1.2 mL N,N-dimethylformamide were added. The resulted solution was stirred at 100 degrees C and 90 degrees C for 10 hours and for 1 hour, respectively. The reaction liquid was diluted with toluene 4 times, and heat-stirred at 100 degrees C for 0.5 hour. Then, 0.3 mL trimethyl(phenyl)tin was added and heat-stirred at 100 degrees C for 8 hours, 1.5 mL bromobenzene was added and heat-stirred at 100 degrees C for 8 hours. The reaction solution was poured in methanol, precipitated and filtered. The obtained solid was dissolved in chloroform, diamine silica gel was added, stirred at room temperature for 1 hour, passed through short column of the acidic silica gel. The resulted product was concentrated, recrystallized using chloroform/ethyl acetate as solvent, and separated by filtration, to obtain 156 mg copolymer.