TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): The preparation of (I) comprises adding raw materials perylene tetracarboxylic imidodicarbonic diamide dibromide and 2,6-ditributyl tin-naphtho(2,1-b: 3,4-b')dithiophene derivative in organic solvent, adding catalyst, carrying out Stille coupling reaction for 24-72 hours at 50-120 degrees C, and refining to obtain copolymer, with mol ratio of perylene tetracarboxylic imidodicarbonic diamide dibromide to 2,6-ditributyl tin-naphtho(2,1-b:3,4-b')dithiophene derivative is at 1:1-1.5:1, and perylene tetracarboxylic imidodicarbonic diamide dibromide of formula (II). The 2,6-ditributyl tin-naphtho(2,1-b:3,4-b')dithiophene derivative is of formula (III). Preferred Components: The organic solvent is tetrahydrofuran, dioxane, glycol dimethyl ether, benzene and/or methyl benzene. The catalyst is organic palladium catalyst or mixture of organic palladium catalyst and organic phosphine ligand; organic palladium catalyst is tris(dibenzylideneacetone)dipalladium(0)/tri(o-tolyl)phosphine, tetrakis(triphenylphosphine)palladium(0) and bis(triphenylphosphine)palladium(II) dichloride; organic phosphine ligand is tri(o-tolyl)phosphine in Stille coupling reaction; and the organic solvent is tetrahydrofuran, glycol dimethyl ether, benzene, chlorobenzene and methylbenzene. Preferred Process: The method comprises adding raw materials perylene tetracarboxylic imidodicarbonic diamide dibromide and 2,6-ditributyl tin-naphtho(2,1-b:3,4-b')dithiophene derivative in organic solvent; adding organic palladium catalyst or mixture of organic palladium catalyst and organic phosphine ligand; and reacting for 30-72 hours at 70-1000 degrees C in inert gas; dropping mixing liquid into alcohol compound, depositing, filtering and washing deposit; dissolving deposit by methylbenzene, adding into water solution, heating at 80-100 degrees C, stirring and reacting for 8-14 hours; separating organic phase in reacting liquid, decompressing and removing organic solvent, and depositing by methanol; and filtering deposit, extracting solid for 2-4 hours, depositing by alcohol compound, and filtering to obtain product.