The effect of hexadecyl groups in 4 position of poly(4H-cyclopenta[2,1-b:3,4-b']dithiophene) was investigated. It was demonstrated that the steric influence of the alkyl-chains controls the structure and therefore the transport properties of the polymers. The characterisation of the electrosynthetized polymer films pointed out the more regular structure of the disubstituted polymer and the higher compactness of the nonsubstituted one. These findings were found to be in agreement with the photoelectric properties of the Schottky junctions between the three different polymers and aluminium. Better performance was achieved in the case of the non-substituted polymer.