Two-dimensional β-phase copper iodide: a promising candidate for low-temperature thermoelectric applications.

Cuprous iodide (CuI), as a p-type semiconductor material, holds significant potential for future electronics that integrate transparent, flexible, and thermoelectric applications. Monolayer β-CuI, once regarded as a high-temperature phase, has recently been successfully synthesized at room temperature. However, its thermoelectric properties remain unexplored. In this work, we systematically investigate the structural stability and the thermoelectric capabilities of monolayer β-CuI and γ-CuI through the density functional theory (DFT) combined with Boltzmann transport theory. Based on the thermoelectric transport coefficients of monolayer β-CuI and γ-CuI, we predict their zT values will vary with carrier concentration and increase with temperature. Comparing the zT values, monolayer β-CuI demonstrates superior thermoelectric properties compared to γ-CuI. At room temperature, the optimal zT values of monolayer β-CuI exceed 1.00 along the Zigzag direction and AC direction. The zT values of γ-CuI at 300 K are 0.25 for n-type and 0.74 for p-type. These results suggest the great potential of the monolayer β-CuI is promising candidate materials for low temperature thermoelectric applications.