TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The electron acceptor is chosen from fullerene, fullerene derivative carbon nanotube, carbon nanotube derivative and semiconductive compound.    TECHNOLOGY FOCUS - POLYMERS - Preparation: No general preparation given. Preferred Properties: The solubility of secondary structural unit is 2-10 times more than solubility of the primary structural unit. The solubility of the copolymer in a solution containing chlorinated solvent, toluene, xylene, trimethyl benzene and tetrahydrofuran is 1-200 mg/ml at room temperature. The number average molecular weight of the copolymer is 500-1000000 g/mol%. The molecular weight distribution of the copolymer is 1-100. Preferred Composition: The structural unit (I) is of formulae (1-1)-(1-3). The secondary structural unit (II) is of formula (2-1) or (2-2). The copolymer comprises a copolymer of formula (III). The layer containing the copolymer is a hole-transport layer and/or hole-injection layer, or electron-injection layer and/or electron-transport layer. The photoactive layer comprises two or more electron donors containing the copolymer and electron acceptors. The electron donor and electron acceptor are bulk heterojunction.R=H, D, halo, nitrile, nitro, imide, amide, hydroxy, or alkyl, cycloalkyl, alkoxy, aryloxy, alkylthio, arylthio, alkyl sulfoxide, aryl sulfoxide, alkenyl, silyl, boron group, alkylamine, aralkyl, amine, arylamine, arylamine or heterocyclyl (all optionally substituted);R15-R18=H, D, halo, nitrile, nitro, imide, amide, hydroxy, or alkyl, cycloalkyl, alkoxy, aryloxy, alkylthio, arylthio, alkyl sulfoxide, aryl sulfoxide, alkenyl, silyl, boron group, alkylamine, aralkyl, amine, arylamine, arylamine or heterocyclyl (all optionally substituted), preferably hydroxy, or 1-40C alkyl, 1-40C alkoxy or 1-40C alkyl sulfoxide (all optionally substituted);andn=1-10000. EXAMPLE - A mixture of 5 mL chlorobenzene, 0.4 g 2,6-bis(trimethyl)-4,8-bis(2-ethylhexyloxy)benzo(1,2-b:4,5-b')dithiophene, 0.1187 g 4,7-bis(5-bromo-2-thienyl)-2,1,3-benzothiadiazole, 0.2141 4,7-bis(5-bromothiophen-2-yl)-5,6-bis(dodecyloxy)benzo(c)(1,2,5)thiadiazole, 14 mg tris(dibenzylideneacetone)dipalladium (0), and 18 mg tri-(o-tolyl)phosphine was reacted at 170 degrees C for 1 hour. The obtained mixture was cooled to room temperature and filtered. The solid was subjected to soxhlet extraction using methanol, acetone, hexane and chloroform . The chloroform portion was re-precipitated in methanol, filtered and copolymer of formula (A) having number average molecular weight of 15000 g/mol and weight average molecular weight of 36200 g/mol was obtained with yield of 32%.    D'=group of formula (D').