Significantly enhanced thermoelectric performance of γ-In2Se3 through lithiation via chemical diffusion

γ-In₂Se₃ is selected as a thermoelectric candidate because it has a unique crystal structure and thermal stability at relatively high temperatures. In this work we have prepared lithiated γ-In₂Se₃ through chemical diffusion and investigated its band structures and thermoelectric performance. After lithiation of γ-In₂Se₃ in lithium acetate (CH₃COOLi) solution at 50oC, we have observed a high Hall carrier concentration (n_H) up to ≤1.71×10¹⁸ cm^-3 at room temperature (RT), which is about ∼4 orders of magnitude compared to that of pristine γ-In₂Se₃. The enhancement in n_H is directly responsible for the remarkable improvement in electrical conductivity, and can be elucidated as the Fermi level (F_r) unpinning and moving towards the conduction band (CB) through the dominant interstitial occupation of Li⁺ in the γ-In₂Se₃ lattice. Combined with the minimum lattice thermal conductivity (κ_L=0.30-0.34 WK^-1m^-1) at ~923 K, the highest ZT value of 0.62-0.67 is attained, which is about 9-10 times that of pristine γ-In₂Se₃, proving that the lithiation in γ-In₂Se₃ is an effective approach on the improvement of the thermoelectric performance.