The morphology and three-dimensional structure of polymer blends can have a profound effect on the optoelectronic properties of polymer blends. To introduce the problem structural studies of a polyfluorene-based blend will be presented with an explanation of the role of casting solvent on photoluminescence properties. The commonly studied blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is discussed in terms of the effect of P3HT composition and molar mass on photovoltaic performance. The addition of a block copolymer to enhance device performance is also presented and discussed. Finally, a presentation of the morphology of a low band gap polymer poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2′,1′,3′-benzothiadiazole] (PCDTBT) on its optical properties is shown. The micro-particulate form is shown to be unsuitable for solar cells.