A Sustainable Brand‐New Thermoelectric Cooling Material: High‐Mobility Diamondoid Cu 3 SbSe 4 Crystal

Diamondoid Cu 3 SbSe 4 is an earth‐abundant thermoelectric material with strong potential for near‐room to mid‐temperature applications. However, its performance has been limited by intrinsically low carrier mobility. Here, we report the first successful growth of large‐sized Cu 3 SbSe 4 crystals, achieving a fivefold enhancement in carrier mobility, and demonstrate the first Cu 3 SbSe 4 ‐based thermoelectric cooling device. We show that Ag substitution reduces both the effective mass and deformation potential through strengthened bond covalency, yielding a high carrier mobility of ∼150 cm 2 V −1 s −1 . This leads to a remarkable power factor of ∼23 µW cm −1 K −2 at 300 K, a maximum ZT of ∼1.6 at 700 K and an average ZT of ∼0.85 over 300–700 K, representing state‐of‐the‐art performance among Cu‐based thermoelectric materials in this temperature range. A 7‐pair device based on Cu 3 SbSe 4 crystal achieves a cooling temperature difference of ∼25 K at room temperature, and reaching a maximum of ∼34 K at 343 K. Additionally, the optimized sample demonstrates a single‐leg power‐generation efficiency of ∼7% at Δ T = 350 K. These results highlight crystal‐growth as a powerful strategy to unlock high‐performance refrigeration in previously limited materials, establishing diamondoid Cu 3 SbSe 4 crystals as a viable, low‐cost and environmentally benign platform for practical thermoelectric applications.