Combining Morphological and Optoelectronic Properties Through Electrochemical Synthesis of P3MT:P3HT Copolymer Films

Combining thiophene derivatives offers a route to improve film morphology while retaining electronic properties relevant to optoelectronic applications. This work investigates electrochemically synthesized poly(3-methylthiophene-co-3-hexylthiophene) (P3MT:P3HT) films in comparison with poly(3-methylthiophene) (P3MT) and poly(3-hexylthiophene) (P3HT) prepared under the same deposition conditions. Films were deposited on fluorine-doped tin oxide (FTO) by galvanostatic electropolymerization with charge control and characterized using electron and atomic force microscopy, Kelvin probe force microscopy, optical spectroscopy, and cyclic voltammetry. The copolymer exhibited a more homogeneous surface than P3MT and an intermediate thickness of 410 ± 45 nm. Its average surface potential was 0.44 V, close to P3MT (0.39 V) and lower than P3HT (0.70 V). An oxidation onset of 0.50 V versus Ag/AgCl and an optical gap of 2.05 eV provided estimated HOMO and LUMO energies of -4.93 and -2.88 eV, respectively. Photoluminescence analysis revealed changes in the relative emission contributions, while the separation between absorption and excitation maxima decreased from 30 nm for P3MT to 11 nm for the copolymer. These results demonstrate that electrochemical copolymerization improves film uniformity while preserving surface potential and oxidation characteristics close to P3MT, combining complementary morphological, optical, and electronic properties for optoelectronic applications.