Extracting electricity from body heat for high-performance organic thermoelectric material

A research group including Associate Professor Masato Nakaya and Professor Jun Onoe of the Graduate School of Engineering at Nagoya University, in collaboration with Associate Professor Satoshi Ogawa of the Institute of Materials and Systems for Sustainability at Nagoya University and Electric Power Development Co., Ltd. (J-POWER), has discovered that combining fullerene molecules with metal oxide nano-clusters yields the world's highest thermoelectric figure-of-merit for an organic thermoelectric material. This discovery is anticipated to promote the widespread use of charge-free, wearable sensor power devices. The results were published in Scientific Reports on March 26.

Thermoelectric devices that convert body heat into electricity are expected to be used as power sources for wearable sensors in an ultra-smart society. To fit these thermoelectric devices tightly against the human body and obtain power from body heat, flexible, lightweight, and high-performance organic thermoelectric materials are essential. The performance of a thermoelectric material is evaluated using the dimensionless figure-of-merit, zT = σα²T/κ, where σ represents the material's electrical conductivity, α is the Seebeck coefficient, T is the absolute temperature, and κ is the thermal conductivity. For practical application, a zT value of 1 or higher is required. However, due to the physical laws of "the trade-off relationship between σ and α" and "the proportional relationship between σ and κ," it has historically been difficult to exceed zT = 0.5.

In this study, the research group achieved zT = 0.81, the world's highest figure of merit for an organic thermoelectric material, by doping a fullerene film with molybdenum oxide nano-clusters. The team fabricated composite films with precisely controlled composition ratios (x = MoO₃/C₆₀) via vacuum co-evaporation of C₆₀ and MoO₃ and evaluated σ and α under vacuum conditions.

As a result, they found that σ improved up to a thousand times compared to a C₆₀ thin film while maintaining an exceptionally large α, and the film exhibited p-type characteristics. Furthermore, when investigating changes in σ and α due to heat treatment of the thin film, the thermoelectric properties remained constant under heating up to approximately 100℃ regardless of the composition x, confirming that the thin film possesses excellent thermal stability as an element material driven at room temperature. Additionally, when the composite films with x = 0.05 and 0.09 were heated at slightly higher temperatures (110-180℃), the power factor (PF) value increased sharply.

Nakaya stated: "We discovered that creating a new material, which could be called a nano-cluster compound, from fullerene (carbon clusters) and molybdenum oxide nano-clusters exhibits extremely excellent thermoelectric properties. We believe that such nano-cluster compounds can be realized using not only molybdenum oxide but also various other metal oxides as building blocks, and we expect to create an unprecedented group of high-performance thermoelectric materials. Furthermore, we anticipate applications not only in thermoelectric materials but also in flexible, high-performance solar cells and electrochemical catalysts."

Journal Information
Publication: Scientific Reports
Title: Novel strategy for boosting thermoelectric performance of organic materials with low electrical conductivity
DOI: 10.1038/s41598-026-44966-8