Fluorinated Copper Phthalocyanine as Interfacial Bridges for High Power Factor n-Type Ta ₄ SiTe ₄ /F _<i>x</i> CuPc/PVDF Flexible Thermoelectric Composites

The rapid development of flexible electronics has attracted a growing interest in flexible thermoelectric materials. Against this background, the development of ternary organic-inorganic composites represents a promising route for improving the thermoelectric (TE) performance and flexibility of materials, especially in systems incorporating one-dimensional (1D) whiskers. Ta₄SiTe₄, a recently identified 1D material, displays exceptional electronic transport properties. However, its composite with insulating poly(vinylidene fluoride) (PVDF) suffers from limited carrier transport. In this study, fluorinated copper phthalocyanines (F_<i>x</i>CuPc) are introduced to fabricate n-type Ta₄SiTe₄/F_<i>x</i>CuPc/PVDF ternary composite films. Characterizations confirm the formation of the F_<i>x</i>CuPc-Ta₄SiTe₄ nanointerface. With increasing fluorine substitution, the energy levels of F_<i>x</i>CuPc shift downward and F₁₆CuPc exhibits a conduction band edge slightly lower than that of Ta₄SiTe₄, enabling efficient electron transfer at the interface and serving as an effective charge transport bridge between adjacent whiskers. This interfacial design simultaneously enhances the electrical conductivity by lowering the contact barrier and increases the Seebeck coefficient through mild carrier concentration modulation and energy-filtering effects. The optimized 50 wt % Ta₄SiTe₄/F₁₆CuPc/PVDF composite film exhibits a 50% enhancement in electrical conductivity over the binary 50 wt % Ta₄SiTe₄/PVDF film, together with a moderate increase in the Seebeck coefficient. Consequently, a maximum power factor of 385.9 μW m^-1 K^-2 is achieved at 5% F₁₆CuPc loading, representing a nearly 50% enhancement compared to the binary 50 wt % Ta₄SiTe₄/PVDF composite (255.6 μW m^-1 K^-2). This work demonstrates an effective molecular design strategy for optimizing carrier transport in organic-inorganic hybrid films toward high-performance flexible thermoelectric applications.