The optimization of thermoelectric performance for Cu₂SnSe₃. (a) Crystal structural transition from monoclinic to cubic due to Cd doping and the local tetrahedral distortion induced by Ag alloying. (b) Schematic diagram illustrating the simultaneous enhancement of carrier mobility and density-of-states effective mass by reducing the deformation potential (ξ) and promoting band convergence (Γ_1V and Γ_2V). (c) Schematic diagram illustrating the decrease in sound velocity (V_ave) due to Ag off-centered behavior. (d) Comparison of carrier concentration (p), carrier mobility (μ), and effective mass (m^*) between pristine Cu₂SnSe₃ and Cu₂Sn_0.9Cd_0.1Se₃. (e) Comparison of average sound velocity, Debye temperature (θ_D) and lattice thermal conductivity (${\kappa }_{\text{lat}}$) between the Cu₂Sn_0.9Cd_0.1Se₃ and Cu_1.85Ag_0.15Sn_0.9Cd_0.1Se₃ compound. (f) Improvement of the maximum ZT value for Cu₂SnSe₃ through Cd doping and Ag alloying.