Enhanced thermoelectric performance of N-type eco-friendly material Cu_1-xAg_xFeS₂ (x=0–0.14) via bandgap tuning

CuFeS₂ is an eco-friendly n-type thermoelectric (TE) material but with poor performance. It is worth noting that the bandgap (E_g) reduction can enhance the carrier mobility (μ_H) which further leads to a higher electrical conductivity (σ) and power factor (PF). Density Functional Theory (DFT) calculation results indicated that Ag dopant in the CuFeS₂ compound can narrow down the E_g. Hence, a series of Cu_1-xAg_xFeS₂ (x = 0–0.14) alloys were prepared by vacuum melting combined with plasma activated sintering to enhance the TE performance via a bandgap tuning route. It can be found that the E_g is indeed shrinking from ∼0.45 to 0.39 eV with the increase of Ag dopant content, and the reduced E_g leads to an obviously enhanced μ_H without carrier concentration decreasing. Due to the elevated μ_H, a higher PF (0.76 × 10⁻³ Wm⁻¹K⁻²) can be obtained and a peak ZT value of 0.45 is achieved at 723 K in Cu_0.88Ag_0.12FeS₂ sample. Therefore, the bandgap tuning can be regarded as an effective strategy for enhancing the TE performance of CuFeS₂.