High Thermoelectric Performance in Cu2SnS3 by Control Over Phase‐Dependent Mobility Edge

Abstract Complex thermoelectric materials composed of multiple phases with order/disorder mixing feature have drawn intense attention due to their high performance. However, some physical mechanisms relevant to thermoelectric properties including the relationship between carrier mobility and disorder extent in these materials are still elusive. Here, a phase‐dependent mobility edge in (Cu 2 Sn 1‐ y S 3 ) 0.85 (CuGaS 2 ) 0.15 solid solutions is demonstrated. By control over the mobility edge in these solid solutions by increasing the ratio of tetragonal phase with less disorder, a weakened localization of electronic states and promoted carrier mobility are realized. Combined with reduced lattice thermal conductivity, a record high zT value of 1.22 is attained at 823 K for (Cu 2 Sn 0.92 S 3 ) 0.85 (CuGaS 2 ) 0.15 with the lowered mobility edge. The findings shed light on a new route to tuning the electrical and thermal transport properties for complex thermoelectric materials with multiple phases.