Defect Driven Electronic Structure Reconfiguration and Hierarchical Phonon Suppression in Ag₂Se Thermoelectrics

Area of Science:

• Materials Science
• Solid State Physics
• Nanotechnology

Background:

• Silver selenide (Ag₂Se) is an n-type thermoelectric material suitable for near-room-temperature applications.
• Enhancing the figure of merit (ZT) of Ag₂Se requires balancing electronic and phononic transport properties.
• Current methods for Ag₂Se modification face challenges in achieving optimal thermoelectric performance.

Purpose of the Study:

• To develop a facile wet-chemical strategy for synthesizing indium-substituted silver selenide (Ag₂Se) nanocrystals.
• To investigate the effects of indium substitution on the electronic structure and thermoelectric properties of Ag₂Se.
• To optimize the synergistic interplay between electronic and phononic transport for improved thermoelectric performance.

Main Methods:

• Facile and controllable wet-chemical synthesis of orthorhombic Ag₂Se nanocrystals under ambient conditions.
• Indium substitution at the Ag site to modulate electronic structure and carrier concentration.
• First-principles calculations to understand the impact of In incorporation on electronic interactions and carrier mobility.

Main Results:

• Indium substitution led to Fermi-level upshift, band-gap narrowing, and increased carrier concentration, enhancing electrical transport.
• In incorporation induced lattice softening and reduced sound velocity, improving phonon scattering and lowering thermal conductivity.
• Ag₁.₉₂₈₇In₀.₀₇₁₃Se achieved a peak figure of merit (ZT) of ~1.2 at 398 K with a high power factor of ~3100 µW m⁻¹ K⁻².
• Prototype modules demonstrated higher output voltage and power density, with improved mechanical resilience.

Conclusions:

• Coupling defect chemistry with electronic structure engineering is an effective strategy for advancing Ag₂Se-based thermoelectrics.
• Indium substitution offers a pathway to simultaneously enhance electrical conductivity and reduce thermal conductivity in Ag₂Se.
• The developed method yields high-performance and mechanically robust thermoelectric materials for practical applications.