First-Principles Predictions of Thermoelectric Figure of Merit for Organic Materials: Deformation Potential Approximation.

We propose a combined computational scheme to predict the thermoelectric properties of organic semiconductors, taking α-form phthalocyanine crystals H2Pc, CuPc, NiPc, and TiOPc as examples. This completely parameter-free approach combines first-principles band structure calculations, Boltzmann transport theory, deformation potential theory for electron-phonon coupling, and nonequilibrium molecular dynamics for heat transport. We abandon the constant relaxation time approximation commonly practiced in the literature. Instead, we calculate it from first principles with the deformation potential approximation. The obtained Seebeck coefficients are in good agreement with experimental results, validating our treatment for relaxation time. From the calculated thermoelectric figure of merit (ZT) value, we show that phthalocyanine crystals could be excellent thermoelectric materials when n-doped, with the highest ZT value of 2.5 in NiPc at a doping level of -1.5 × 10(20) cm(-3).