Optoelectronic nature of carriers in polypyrrole-coated lignocellulose nanofibrils revealed by a combination of terahertz and far-infrared transmission spectroscopy

An elaborate combination of terahertz time-domain spectroscopy and Fourier transform infrared spectroscopy in transmission geometry is employed to investigate the optoelectronic nature of carriers in polypyrrole-coated lignocellulose nanofibrils (PPy@LCNF). The PPy@LCNF nanocomposite has a core-shell structure for each individual fibril and is made into two films with lightly and heavily protonated polypyrrole. Both spectral features of terahertz complex conductivity and terahertz/infrared transmittance are well reproduced by an extended Drude model in a consistent way, describing the partial localization of carriers. The carriers in the heavily protonated PPy@LCNF film are found to have a lower localization degree as well as a higher density than those in the lightly protonated one.