Band Engineering via Charge Modulation Drives High Thermoelectric Performance in Conductive MOFs.

Metal-organic frameworks (MOFs) are promising thermoelectric materials due to their low lattice thermal conductivity and tunable electronic properties. However, many conductive MOFs exhibit metallic behavior, leading to low Seebeck coefficients and high electronic thermal conductivity, which limit thermoelectric efficiency. We propose a band-engineering approach based on controlled charge modulation to tune the electronic structure by modifying the oxidation state of the metal centers. Using copper benzenehexathiol (CuBHT) as a model MOF, density functional theory, electron-phonon coupling, and Boltzmann transport calculations show that adjusting Cu+/Cu2+ states triggers a metal-to-semiconductor transition with a band gap, boosting the Seebeck coefficient and reducing electronic thermal conductivity. This increases zT by nearly 2 orders of magnitude. Further, optimization via 5% compressive strain increases the Seebeck coefficient to about 250 μV K-1 at 300 K (10 times higher than pristine) and achieves a maximum zT of 0.79 at 550 K, approaching the performance of established thermoelectric materials and surpassing most reported MOF-based systems.