Thermoelectric properties ofp-type CuInSe2chalcopyrites enhanced by introduction of manganese

Thermoelectric properties, x-ray photoelectron spectroscopy, Raman spectroscopy, and electronic structures have been studied for Mn-substituted CuInSe${}_{2}$ chalcopyrites. Raman spectroscopy verifies the lattice disorder due to the introduction of Mn into the CuInSe${}_{2}$ matrix, leading to a slight suppression of thermal conductivity. On the other hand, the Mn substitution significantly increases the electrical conductivity and Seebeck coefficient. Therefore the thermoelectric figure of merit $ZT$ has been enhanced by over two orders of magnitude by the introduction of Mn into CuInSe${}_{2}$. These materials are $p$-type degenerate semiconductors, containing divalent Mn species as confirmed by x-ray photoelectron spectroscopy. The crystal structure of Mn-substituted CuInSe${}_{2}$, as well as related ternary and quaternary diamond-like semiconductors, can be viewed as a combination of an electrically conducting unit, the Cu-Se and Mn-Se networks, and an electrically insulating unit, the In-Se network. Therefore, diamond-like semiconductors can serve as a potential class of thermoelectric materials with relatively wide band gaps upon substitution with Mn or other transition metals.