A facile electrochemical method to prepare thiophene oligomers has been developed. The synthesis was conducted by terminating a growing macromolecular chain with bromine radicals. This method is based on the proximity of the polymerization potential of 2,2'-bithiophene (BT) and the oxidation potential of bromide. Layers of short thiophene oligomers can be deposited by increasing concentration of bromide in the electrolyte solution. The characteristic UV-vis absorbance maximum shifted consistently to the bromide concentration, which suggests the possibility of accurately turning the optical band gap of electrodeposited material. This method is versatile and has also been successfully applied to synthesize 3,4-ethylenedioxythiophene (EDOT) oligomers. The layer of electrodeposited EDOT oligomers was incorporated as a hole transporting layer in a polymer solar cell to test its performance in a functional device. (C) 2012 Elsevier Ltd. All rights reserved.