The ability to convert waste heat into electricity is important for wearable electronic devices, and thermoelectric conjugated polymers, with their flexibility and low cost, would be great material candidates for these applications. However, their thermoelectric figure of merit, which measures their ability to convert heat gradients into electricity, has so far been consistently below 0.5, whereas applications require a value of around 1. Now, writing in Nature, Chong-an Di and collaborators present a polymeric thermoelectric material with a figure of merit of 1.28 at 368 K.

“We took inspiration from the early success of inorganic superlattice structures,” explains Di. “After 5 years of attempts, we concluded that such geometries are not suitable for polymers due to the challenge of achieving highly crystalline films and atomically flat interfaces, so we reversed our design approach and created the PMHJ instead, which incorporates two less-crystalline films with a blending interface.” One of the challenges was the precise characterization and manipulation of the structure. “Initially, we were unable to determine the exact structure of the PMHJ because typical techniques destroy the film during visualization; thus, we could enhance the figure of merit, but only to a value of 0.8,” shares Di. “We eventually discovered that time-of-flight secondary ion mass spectrometry could be used to characterize the PMHJ: once this issue was resolved, we were able to fine-tune the structure and achieve a figure of merit exceeding 1.2.”