The intent of this master thesis is to improve the power conversion efficiency of polymer solar cells by controlling the morphology of the active layer. By employing block copolymers, which are well known for their ability to phase separate in a nanometer scale, it should be possible to control the morphology. Polymers with electron donating and accepting properties were chosen on the basis of the size of their band gaps as well as the relative positions of their LUMO levels in order to maximize the solar cells performance. Poly(5,7-bis(2-thienyl)-2,3-bis(3,5-bis(2-ethylhexyloxy)phenyl)thieno[3,4-b]pyrazine) and poly(3-cyano-4-hexylthiophene) were chosen as donor and acceptor polymers respectively. None of the polymers could be synthesized due to problems with the synthesis and purification of the monomers. Grignard Metathesis was attempted for polymerization, but an inactive catalyst offered no polymers. Instead, three copolymers were synthesized by Suzuki coupling. Their properties were tested with UV/vis spectroscopy, gel permeation chromatography and in polymer solar cells with [6,6]-phenyl-C61-butyric acid methyl ester as electron acceptor. Of the three polymers the novel polymer of 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester and 5,5’’-dibromo-3’,4’-dinitroterthiphene resulted in the highest efficiency of 0.011 %