Electro-optical properties of electropolymerized poly(3-hexylthiophene)/ carbon nanotube composite thin films

3-hexylthiophene was electropolymerized on a carbon nanotube (CNT)-laden fluorine-doped tin oxide substrate. Scanning electron microscopy and Raman spectroscopy revealed that the polymer was infused throughout the thickness of the 150-nm thick CNT mat, resulting in a conducting composite film with a dense CNT network. The electropolymerized poly(3-hexylthiophene) (e-P3HT)/CNT composites exhibited photoluminescence intensity quenching by as much as 92% compared to the neat e-P3HT, which provided evidence of charge transfer from the polymer phase to the CNT phase. Through-film impedance and J-V measurements of the composites gave a conductivity (σ) of 1.2 × 10^-10 S cm^-1 and zero-field mobility (μ₀) of 8.5 × 10^-4 cm² V^-1 s^-1, both of which were higher than those of neat e-P3HT films (σ = 9.9 × 10^-12 S cm^-1, μ₀ = 3 × 10^-5 cm² V^-1 s^-1). In electropolymerized samples, the thiophene rings were oriented in the (010) direction (thiophene rings parallel to substrate), which resulted in a broader optical absorbance than for spin coated samples, however, the lack of long-range conjugation caused a blueshift in the absorbance maximum from 523 nm for unannealed regioregular P3HT (rr-P3HT) to 470 nm for e-P3HT. Raman spectroscopy revealed that π-π stacking in e-P3HT was comparable to that in rr-P3HT and significantly higher than in regiorandom P3HT (ran-P3HT) as shown by the principal Raman peak shift from 1444 to 1446 cm^-1 for e-P3HT and rr-P3HT to 1473 cm^-1 for ran-P3HT. This work demonstrates that these polymer/CNT composites may have interesting properties for electro-optical applications.