Strategic vacancy engineering advances record-high ductile AgCu(Te, Se, S) thermoelectrics

AgCu(Te, Se, S) alloys, as one of the rare p-type plastic inorganic thermoelectrics, are receiving striking attention for their application foreground in high-performing flexible thermoelectric generators. However, strategies to enhance their thermoelectric performance while maintaining exceptional plasticity remain largely unexplored. Here, we introduce a strategic vacancy-engineering approach to address this challenge. Using computational design as a guide, we carefully tune the cation vacancy concentration to optimize hole carrier concentration, achieving impressive ZTs of ~0.62 at 300 K and ~0.83 at 343 K in (AgCu)_0.998Te_0.8Se_0.1S_0.1, ranking among the highest in this class of material. Importantly, numerous diffuse Ag-S bonds combined with amorphous phase introdeuced by vacancy engineering ensure that (AgCu)_0.998Te_0.8Se_0.1S_0.1 retains high plasticity while having high performance. A novel flexible thermoelectric device, comprising ductile p-type (AgCu)_0.998Te_0.8Se_0.1S_0.1 and n-type commercial Bi₂Te₃, achieves an impressive power density of ~126 μW cm^-2 under 25 K temperature difference, demonstrating significant application prospects for wearable electronics.