Quantitative evaluation of thermoelectric characteristics of small-molecule organic semiconductors based on electronic structure calculations

Organic thermoelectric materials have attracted much attention as prominent candidates for flexible power generators. However, molecular design strategies are not well established. Targeting this problem, we propose a calculation method for quantitative evaluation of thermoelectric properties of organic semiconductors (OSCs) which facilitates the exploration of novel organic thermoelectrics. Ohno (one of the present authors) and his collaborators have shown that the Seebeck coefficients of crystalline OSCs can be calculated from the DOS measured experimentally using the Mott formula[1], so we evaluated effective DOS of bulk OSCs. By conducting classical molecular dynamics simulations followed by electronic structure calculation, the thermally induced structural fluctuation was taken into account and the DOS of bulk crystal was well approximated. The values of Seebeck coefficients estimated from DOS were 0.26 mV/K for pentacene and 0.17 mV/K for rubrene. These values agree quantitatively with experimental results[2]. In the presentation, relationships between structures and thermoelectric properties will also be discussed in depth.

[1] S. Watanabe and M. Ohno et al., Phys. Rev. B 100, 241201(R) (2019). [2] K. P. Pernstich et al., Nat. Mater. 7, 321 (2008).