Interfacial-State and Transport-Barrier Competition in Electrochemically Deposited PANI Nanocomposites: A Unified Theoretical Framework for Bandgap Evolution, Disorder, Dielectric Dispersion, Nonlinear Optics, and DC Conductivity

This review analyzes electrochemically deposited polyaniline (PANI) nanocomposite thin films containing metallic, semiconducting, and dielectric fillers, including Ag/PANI, Mo/MoOx/PANI, CeO2/PANI, Fe2O3/PANI, Al2O3/PANI, CuO/PANI, Co3O4/PANI, and CoFe2O4/PANI. The work examines how filler chemistry and loading influence optical-gap evolution, Urbach disorder, dielectric dispersion, nonlinear optical response, structural coherence, and dc conductivity under comparable electrochemical growth conditions. The comparative analysis shows that optical-gap narrowing and conductivity enhancement are not necessarily coupled. Ag/PANI exhibits simultaneous optical softening and improved conductivity, consistent with metallic bridging, dielectric screening, and enhanced charge connectivity. In contrast, Mo/MoOx/PANI shows strong optical-gap reduction but reduced conductivity, indicating that optically active interfacial states may remain localized or mobility-limiting. Oxide fillers produce additional regimes: CeO2/PANI can suppress Urbach disorder and microstrain through order stabilization, whereas Al2O3/PANI may widen higher-energy transitions and reduce transport through wide-gap barrier effects. Based on these contrasts, a unified framework is proposed that separates the interfacial electronic function from the transport-connectivity function. This approach classifies PANI nanocomposites into transport-assisted metallic, mobility-limiting interfacial, order-stabilized oxide, and barrier-dominated dielectric regimes, providing practical criteria for selecting filler type and loading windows in optoelectronic, sensing, and photonic applications.