n-Type thermoelectric materials based on CuTCNQ nanocrystals and CuTCNQ nanorod arrays

Abstract

We report the synthesis and thermoelectric (TE) performance of organometallic coordination polymers, including copper 7,7,8,8-tetracyano-p-quinodimethane nanocrystals (NC-CuTCNQ) and thin films of CuTCNQ nanorod arrays (NrA-CuTCNQ). The characterization of NC-CuTCNQ was carried out with the compressed samples. For NrA-CuTCNQ films, the TE properties were investigated with a hybrid Au/Cu/CuTCNQ/Au architecture along the direction either vertical or parallel to the film surface and obviously anisotropic behaviors were observed. We found that CuTCNQ can be a potential n-type material for future application in thermoelectric devices with a power factor of 1.5 μW m⁻¹ K⁻², accompanied by a high Seebeck coefficient of −632 μV K⁻¹ at 370 K. In order to optimize its TE performance, a cousin molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄TCNQ) was mixed with TCNQ reacted with CuI. We found that the CuTCNQ blend possessed the highest power factor of 2.5 μW m⁻¹ K⁻² with a 1 mol% blend ratio of F₄TCNQ (related to TCNQ) at 370 K.