Hirotaka Kojima

From materials to device design of a thermoelectric fabric for wearable energy harvesters

We propose a design and fabrication process for fabrics containing thermoelectric generators (TEGs) in the form of carbon nanotube composite threads intended for energy harvesting of low-temperature waste heat. Our prototype thermoelectric fabric with an integrated p/n-stripe-patterned CNT thread shows potential as an easy-to-use power source for wearable electronics.

Giant Seebeck effect in pure fullerene thin films

The small thermal conductivity of molecular solids is beneficial for their thermoelectric applications. If Seebeck coefficients were sufficiently large to compensate for the relatively small electrical conductivity, these materials would be promising candidates for thermoelectric devices. In this work, the thermoelectric properties of C60 were studied by in situ measurements under ultrahigh vacuum after the deposition of a pure C60 thin film. An exceptionally large Seebeck coefficient of more than 150 mV/K was observed as a steady-state thermoelectromotive force. Even considering several extreme but realistic conditions, conventional semiclassical thermoelectric theories cannot explain this giant Seebeck effect.

Universality of the giant Seebeck effect in organic small molecules

To explore the universality of the giant Seebeck coefficient (>100 mV K−1) found in our previous study with pure C60 thin films, the thermoelectric properties of high-mobility small-molecule organic semiconductors and their temperature dependencies are investigated. Consequently, various pure organic semiconductors exhibited similar large Seebeck coefficients within the temperature range of 300–360 K. The magnitude of the Seebeck coefficient, its intense temperature dependence, and correlation with the activation energy of electrical conductivity are unique and cannot be elucidated by currently known physical models of thermoelectricity.