Abstract The growth, structure and morphology of polyterthiophene films has been characterised using a range of electrochemical and structural techniques. The kinetics of the growth process, including the diffusion coefficient of the terthiophene monomer and the rate constant of the polymerization process has been measured. The electrochemical analysis is consistent with a Stranski–Krastanov growth mode involving the completion of a dense precursor layer prior to the growth of a more porous bulk overlayer. Fabricating polyterthiophene films under diffusion-controlled conditions appears to maximise the thickness of the dense precursor layer. The implication of these results on the photovoltaic energy conversion efficiency of photoelectrochemical cells fabricated from electropolymerized terthiophene is discussed.