TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The photovoltaic device has bulk heterojunction structure including conjugated polymer, and fullerene.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The fullerene is methyl(6,6)-phenyl-61C-butyrate or methyl(6,6)-phenyl-71C butyrate. The 3,6-bis(selenophen-2-yl)-1H,2H,4H,6aH-pyrrolo(3,4-c)pyrrole-1,4-dione-containing repeating unit is preferably of formula (IV) and (V).R1,R2=alkyl or aryl (both optionally substituted).    TECHNOLOGY FOCUS - POLYMERS - Preparation (claimed): The conjugated polymer is prepared by copolymerizing donor moiety-containing monomer of formula: X-D'-X (II), and 3,6-bis(selenophen-2-yl)-1H,2H,4H,6aH-pyrrolo(3,4-c)pyrrole-1,4-dione derivative monomer (III).X=boronic acid, boronate, magnesium halide, zinc halide or trialkyl tin (when Y' is Cl, Br or I), or Cl, Br, or I (when Y' is boronic acid, boronate, magnesium halide, zinc halide or trialkyl tin). Preferred Definitions:    D'=group of formula (i) or (ii);and    R=H, halo, cyano, nitro, or alkyl, aryl or heteroaryl (all optionally substituted).    EXAMPLE - 0.236 g 2,6-Bis(trimethyltin)-4,8-bis(5-decyl-2-thienyl)-benzo(1,2-b:4,5-b')dithiophene and 0.1952 g 2,5-di(2-octyldodecyl)-3,6-bis-(5-bromoselenophenyl)-1,4-diketopyrrolo(3,4-c)pyrrole were dissolved in 10 mL toluene and 1 mL dimethylformamide in a flask protected by argon. The solution was flushed with argon for 10 minutes, and 10 mg tetrakis(triphenylphosphine)palladium(0) was added to the flask. The solution was flushed with argon again for 10 minutes. The oil bath was heated to 115?o C, and reaction mixture was stirred at 115?o C for 8 hours under argon atmosphere. Then, the mixture was cooled to room temperature, polymer was precipitated in 100 ml methanol, precipitated solid was collected and purified by silica gel chromatography using chloroform as eluent, to obtain ethylhexylthienylbenzo-dithiophene-alt-2,5-bis(2-butyloctyl)-3,6-bis(selenophene-2-yl)pyrrolo(3,4-c)pyrrole-1,4-dione-containing polymer of formula (Ia) as dark green-purple solid with yield of 56%.    R11=2-butyloctyl;and    R12=2-ethylhexyl.