Engineering coordination polymers with ethenetetrathiolate ligand for versatile thermoelectric thin films and planar modules

Coordination polymers based on ethenetetrathiolate ligands are promising materials for developing innovative thermoelectric technologies as they combine intrinsic electrical conductivity, favorable Seebeck coefficients, and potentially reduced reliance on scarce and critical raw materials. However, their integration into planar and flexible modules remains constrained by processability and device-engineering challenges. Here, we investigate complementary p-type poly[Kx(Cuett)] and n-type poly[Kx(Niett)], through a combined experimental and theoretical study aimed at developing thermoelectric modules. The two polymers are solution-processed without additives or post-treatments, enabling their direct deposition as thin films. Films exhibit suitable electrical conductivity and complementary thermoelectric responses. Molecular modeling links the charge-transport behavior to the metal-dependent electronic structure and reproduces the experimental Seebeck coefficients. Their complementary thermoelectric behavior, combined with solution processability, enable integration into planar p-n modules on different substrates, including glass, flexible PET, and low-cost paper. Thermoelectric modules exhibit Seebeck coefficients of 150-230 μV/K in the 20-60 °C range, consistent with the additive contribution of the individual legs. Additionally, the unencapsulated modules show remarkable mechanical and long-term ambient stability. These findings demonstrate that coordination polymers based on ethenetetrathiolate ligands, combining facile synthesis with additive-free, low-temperature solution processing, offer a promising platform for the development of versatile and more sustainable thermoelectric devices for low-grade energy conversion.