Synergistic Cd and In co-doping enables high thermoelectric performance in p-type AgBiSe₂

p-type AgBiSe₂ thermoelectric materials have attracted considerable attention due to their intrinsically ultralow lattice thermal conductivity and favorable valence band characteristics. However, their thermoelectric performance is severely limited by the low intrinsic hole concentration and inefficient doping. Here, we substantially improve the thermoelectric performance of p-type AgBi_1−xCd_xIn_xSe₂ through synergistic co-doping of Cd and In. The room-temperature hole concentration is effectively increased from ∼2.1 × 10¹⁷ cm⁻³ in pristine AgBiSe₂ to ∼3.5 × 10¹⁹ cm⁻³ in AgBi_0.92Cd_0.04In_0.04Se₂, leading to a significant enhancement in electrical conductivity and power factor. First-principles calculations reveal that co-doping induces pronounced valence band flattening and band convergence, resulting in a high density-of-states effective mass. Additionally, Cd and In co-doping reduces the lattice thermal conductivity for x ≤ 0.03, while an anomalous increase is observed for x = 0.04. Consequently, a peak zT of ∼0.6 at 448 K and an average zT of ∼0.5 across the temperature range of 303–473 K are achieved. This work demonstrates that co-doping represents an effective synergistic strategy for simultaneously optimizing carrier concentration and band structure in p-type AgBiSe₂, providing a viable pathway for the development of low-temperature thermoelectric materials.