Electronic Structure, Doping Effects, and Charge Transport in Conjugated Polymer Nanocomposites: Insights from UV-Vis Spectroscopy and AC/DC Conductivity Measurements

Abstract This review focuses specifically on metal salt–doped PNCs, analyzing how dopant type and concentration influence key parameters such as electronic conductivity, optical bandgap, refractive index, and dielectric permittivity. Reported findings consistently show that higher dopant concentrations narrow the optical bandgap, thereby facilitating electronic transitions, while also enhancing the refractive index through increased polarization of the polymer chains. Electrical measurements reveal that DC conductivity rises with temperature in a thermally activated manner, attributed to phonon-assisted hopping of charge carriers within low-dimensional transport pathways. Dielectric studies indicate that the dielectric constant (ε_r) decreases with increasing frequency, stabilizes at high frequencies, and increases with temperature. Conducting polymers such as polyaniline (PANI) exemplify these structure–property relationships, underscoring the suitability of doped PNCs for sensors, energy storage, microbial detection, displays, and photovoltaic devices. By consolidating and comparing these results, the review provides a framework for understanding how metal salt doping governs the interplay between optical and electrical characteristics in polymer nanocomposites, thereby guiding the rational design of advanced functional materials.