Highly efficient thermoelectric converters based on metalloporphyrin nanotubes†

Novel devices based on porphyrin nanotubes may lead to a wide range of uses in electronic functionality and thermoelectric conversion. π-Conjugated metallo-porphyrin nanotubes have been designed with a configuration of oppositely charged porphyrin molecules, which leads to oscillatory bandgaps as a function of the diameter of the nanotube. We focus in this work on bottom-up porphyrin nanotubes, rather different from conventional carbon nanotubes, making them favorable candidates as precursors for nanotube devices. We exploited the asymmetric band gap feature to design configurations of stacked six-metalloporphyrin rings connected by butadiyne to form a periodic nanotube structure with different metallic atoms (Zn, Fe, and Fe–Cl). The electronic transport properties given by the transmission coefficients show that porphyrin nanotubes with Zn produce step-like features located asymmetrically relative to the Fermi energy (E_F), which lead to huge enhancements of the thermoelectric performance. The highest values obtained for the thermopower and the electronic figure of merit can also be obtained for many different positions of E_F, which makes Zn-porphyrin nanotubes an optimal candidate for designing novel thermoelectric devices.