Efficient Colloidal Dispersion of Poly(nickel-ethenetetrathiolate) in Aqueous-organic Solvents for Solution-processed Organic Thermoelectrics

Abstract

Coordination polymers are promising candidates for thermoelectric applications, yet their practical use is often limited by poor solubility and processability. Here, we report a spontaneous and efficient dispersion strategy for poly(nickel-ethenetetrathiolate) sodium salt (poly(Nax[NiETT])) in aqueous-organic mixed solvents, enabling the fabrication of robust, binder-free thin films composed of neutral poly[NiETT] species. These films exhibit excellent thermoelectric performance, achieving electrical conductivities up to 47 S cm⁻¹, Seebeck coefficients of –74 to –130 μV K⁻¹, and power factors up to 47 μW m⁻¹ K⁻². Structural and elemental analyses reveal the reduction of the oxidized precursor to the neutral state during dispersion. Importantly, we demonstrate that environmental humidity effectively modulates the n-type doping level and thermoelectric performance. Furthermore, we highlight the application of these films in photothermoelectric THz sensors, where they achieve up to four-fold enhanced sensitivity compared to CNT-only devices. This work provides a general strategy for processing otherwise insoluble coordination polymers and opens new opportunities for solution-processed energy and sensing materials.