Toward Ultrahigh Thermoelectric Performance of Cu₂SnS₃‐Based Materials by Analog Alloying

Abstract Cu₂SnS₃ is a promising thermoelectric candidate for power generation at medium temperature due to its low‐cost and environmental‐benign features. However, the high electrical resistivity due to low hole concentration severely restricts its final thermoelectric performance. Here, analog alloying with CuInSe₂ is first adopted to optimize the electrical resistivity by promoting the formation of Sn vacancies and the precipitation of In, and optimize lattice thermal conductivity through the formation of stacking faults and nanotwins. Such analog alloying enables a greatly enhanced power factor of 8.03 µW cm⁻¹ K⁻² and a largely reduced lattice thermal conductivity of 0.38 W m⁻¹ K⁻¹ for Cu₂SnS₃ – 9 mol.% CuInSe₂. Eventually, a peak ZT as high as 1.14 at 773 K is achieved for Cu₂SnS₃ – 9 mol.% CuInSe₂, which is one of the highest ZT among the researches on Cu₂SnS₃‐based thermoelectric materials. The work implies analog alloying with CuInSe₂ is a very effective route to unleash superior thermoelectric performance of Cu₂SnS₃.