Enhanced thermoelectric performance of phthalocyanine complexes/single-walled carbon nanotube hybrids by tuning the types of metal coordination ions

Abstract

Herein, three hybrids of metal Phthalocyanine complexes (MPc, M=Ni, Cu, Co) with single-walled carbon nanotubes (SWCNTs) were prepared by ball milling combined with cold pressing method and their thermoelectric (TE) properties were studied. The electrical conductivity of the MPc/SWCNT hybrids remarkably increased with increasing SWCNT content and was higher than the values calculated based on the mixture rule, whereas the Seebeck coefficient slightly decreased in the whole range. Moreover, the NiPc/SWCNT hybrids showed higher electrical conductivity than those of CuPc/SWCNT and CoPc/SWCNT hybrids. It is demonstrated by Raman analyses and energy level measurement that strong donor-acceptor interactions occur between MPc and SWCNTs. Such interactions may promote the carrier transport at the interface, and therefore increase the carrier mobility resulting in the enhancement of electrical conductivity greatly overstepping the mixture rule. Furthermore, among the three hybrids, the interface energy barrier of NiPc/SWNT hybrids is the lowest, which also contributes to the high electrical conductivity. Finally, the maximum electrical conductivity and thermoelectric power factor of NiPc/SWCNT hybrids are up to 540 S cm−1 and 120 μWm−1 K−2 respectively, which is 30–50% higher than those of CuPc/SWCNT and CoPc/SWCNT hybrids and among the best level of metal-organic small molecules based TE materials.