Progress in Nickel‐Coordinated Polymers as Intrinsically Conducting n‐Type Thermoelectric Materials

Abstract

AbstractOrganic thermoelectrics have witnessed rapid development in the past decade for low temperature energy harvesting applications. While high‐performance p‐type polymers have been demonstrated, n‐type materials have lagged behind due to the limited number of stable n‐dopants and low doping efficiencies. Nickel‐coordination polymers are a promising class of n‐type polymers as they are conducting without extrinsic doping, thus overcoming a major challenge. However, advantages in thermoelectric properties are outweighed by a complicated synthesis and a poorly understood reaction mechanism that has resulted in a large variation in literature for the same material. This progress report provides a comprehensive and critical overview of syntheses and thermoelectric property optimization approaches for two coordination polymers, namely Ni‐ethenetetrathiolate (NiETT) and Ni‐tetrathiooxalate (NiTTO). In particular, material characterization and thin film fabrication techniques are discussed, and the importance of reporting statistically relevant thermoelectric properties is highlighted to ensure reproducibility among different groups. A short discussion on prototype devices based on NiETT is presented, and finally, directions for future development of these and other n‐type metal‐coordinated polymers are suggested.