Thermoelectric power factor of TTT2I3 quasi-one-dimensional crystals in the 3d physical model

Abstract

Tetrathiotetracene – Iodide organic crystals (TTT2I3) are very promising materials for thermoelectric applications. Due to their pronounced quasi-one-dimensionality, the density of states is increased in the direction of molecular chains and, respectively, the Seebeck coefficient is also increased. In addition, partial compensation of two main electron-phonon interactions leads to significant increase of carriers’ mobility, ensuring high values of electrical conductivity. However, the mobility is diminished by the scattering on impurities and by the interchain interaction. Theoretically, it was predicted a power factor values up to 0.03 W/m•K2 for crystals with increased purity. Initially, the estimations were performed in the frame of a simplified one-dimensional (1D) model, neglecting the weak interchain interaction. Further investigations have shown that for ultra-pure crystals this interaction becomes important and the calculations should be performed in the frame of a more realistic 3D model. In this paper, the electrical conductivity, Seebeck coefficient and the power factor for TTT2I3 organic crystals are presented in a 3D model. Also, the criteria of applicability of the simplified 1D model are estimated.