In a significant breakthrough for flexible electronics, researchers have enhanced the thermoelectric properties of AgCu(Te, Se, S) alloys, making them a compelling candidate for high-performance thermoelectric devices.
This advancement is critical as traditional thermoelectric materials often suffer from brittleness, limiting their application in flexible devices. By employing a strategic vacancy-engineering approach, the research team optimized the cation vacancy concentration, leading to improved hole carrier concentration.
The newly developed alloy, termed (AgCu)0.998Te0.8Se0.1S0.1, demonstrated impressive thermoelectric performance, achieving a ZT value of approximately 0.62 at 300 K and 0.83 at 343 K—placing it among the best performing p-type thermoelectrics in its class. The researchers attributed the enhanced performance to a unique combination of diffuse Ag-S bonds and an amorphous phase introduced through vacancy engineering, which allowed the material to maintain high plasticity.
Under practical testing conditions, a flexible thermoelectric device comprising the ductile (AgCu)0.998Te0.8Se0.1S0.1 and n-type commercial Bi2Te3 legs achieved a power density of around 126 μW cm−2 with an applied temperature difference of 25 K. This result underscores the alloy's potential for applications in wearable electronics, where adaptability and efficiency are crucial.
The challenge was to improve the thermoelectric properties while preserving the alloy's exceptional ductility. The research team utilized computational design to introduce selenium at the telluride sites in the AgCuTe lattice, successfully reducing the content of the secondary phase α-Ag2Te. This adjustment led to a decrease in hole carrier density from 9.8 × 1018 cm−3 in undoped AgCuTe to 6.5 × 1018 cm−3 in the modified alloy, yet significantly boosting the ZT value to 0.12 at 343 K.
Further enhancements were achieved by integrating sulfur into the composition, which improved solubility and carrier concentration, fine-tuning the properties to yield (AgCu)0.998Te0.8Se0.1S0.1. This composite showcased a notable engineering strain increase from approximately 1% to 10% in standardized bending tests.
Research employed first-principles density functional theory (DFT) calculations to clarify how the incorporation of (Se, S) and the engineering of vacancies affect the thermoelectric properties. X-ray diffraction analyses confirmed the hexagonal phase of the pristine AgCuTe while highlighting the effective suppression of the α-Ag2Te phase through selenium doping.
Additionally, mechanical properties were rigorously assessed, demonstrating that the addition of sulfur forms multi-center Ag-S bonds, which significantly enhance the mechanical strength and ductility of the alloys.
The flexibility of (AgCu)0.998Te0.8Se0.1S0.1 has been highlighted through its excellent performance in bending tests, where it successfully maintained functionality even under physical strain.
The production of a flexible in-plane thermoelectric device from these alloys marks a considerable advancement in the field, particularly for integration into wearable technologies. The findings suggest that the prepared device demonstrates not only remarkable thermoelectric and mechanical properties but also stability, which is essential for devices expected to operate in real-world conditions.
The research, funded through the Australian Research Council, outlines a novel path toward developing sustainable energy solutions that can effectively convert heat to electricity without the negatives associated with traditional methods.
