Systematic Power Factor Enhancement in n‐Type NiETT/PVDF Composite Films

Abstract

Abstract Nickel ethenetetrathiolate (NiETT) coordination polymers are shown to exhibit high thermoelectric performance as pressed pellets. Because the material is insoluble, films are formed by fabricating a composite of the material in an inert polymer matrix, a process that adversely impacts thermoelectric properties. To date, a reliable and reproducible synthesis has not been reported, which was the motivation for a systematic study of the substeps involved to understand the reaction mechanism. The results of these studies yield optimized reaction conditions for high performance n‐type films, which are derived from empirical studies and material characterization. Herein, a reaction procedure is presented that gives reproducible properties when preparing batches in the 0.5–15 g range. The identity of the counterion, nickel equivalency, and oxidation extent are investigated, which provide insight into the synthetic reaction mechanism and the ligand‐centered oxidation process in these polymers. Optimized materials based on Na[NiETT] exhibit one of the highest n‐type thermoelectric performance for solution‐processed films reported to date, with power factors of 23 µW (m K) −2 (due to conductivities approaching 50 S cm −1 ) while maintaining their stability in ambient conditions.