Development of n-type cobaltocene-encapsulated carbon nanotubes with remarkable thermoelectric property

Direct conversion from heat to electricity is one of the important technologies for a sustainable society since large quantities of energy are wasted as heat. We report the development of a single-walled carbon nanotube (SWNT)-based high conversion efficiency, air-stable and flexible thermoelectric material. We prepared cobaltocene-encapsulated SWNTs (denoted CoCp 2 @SWNTs) and revealed that the material showed a negative-type (n-type) semiconducting behaviour (Seebeck coefficient:-41.8 μV K^-1 at 320 K). The CoCp 2 @SWNT film was found to show a high electrical conductivity (43,200 S m^-1 at 320 K) and large power factor (75.4 μW m^-1 K^-2) and the performance was remarkably stable under atmospheric conditions over a wide range of temperatures. The thermoelectric figure of merit (ZT) value of the CoCp 2 @SWNT film (0.157 at 320 K) was highest among the reported n-type organic thermoelectric materials due to the large power factor and low thermal conductivity (0.15 W m^-1 K^-1). These characteristics of the n-type CoCp2@SWNTs allowed us to fabricate a p-n type thermoelectric device by combination with an empty SWNT-based p-type film. The fabricated device exhibited a highly efficient power generation close to the calculated values even without any air-protective coating due to the high stability of the SWNT-based materials under atmospheric conditions.