Disclosed is a polymer blend comprising an organic semiconductor (OSC) polymer blended with an isolating polymer and method for making the same. The OSC polymer includes a diketopyrrolopyrrole fused thiophene polymeric material, and the fused thiophene is beta-substituted. The isolating polymer includes a non-conjugated backbone, and the isolating polymer may be one of polyacrylonitrile, alkyl substituted polyacrylonitrile, polystyrene, polysulfonate, polycarbonate, an elastomer block copolymer, derivatives thereof, copolymers thereof and mixtures thereof. The method includes blending the OSC polymer with an isolating polymer in an organic solvent to create a polymer blend and depositing a thin film of the polymer blend over a substrate. Also disclosed is an organic semiconductor device that includes a thin semiconducting film comprising OSC polymer.