High-performance thermoelectric properties of oriented and non-stoichiometric AgSnTe2 thin film

Abstract

This work studies the thermoelectric behavior of oriented, non-stoichiometric AgSnTe₂ thin films, focusing on how post-annealing influences their structural and electrical characteristics. Deviations from stoichiometry introduce a higher density of intrinsic point defects and facilitate the emergence of secondary phases, both of which play a critical role in charge carrier dynamics. Post-annealing significantly enhances electrical conductivity by improving grain connectivity and introducing additional charge transport pathways. Thermal treatment at 673 K leads to a pronounced rise in the Seebeck coefficient, increasing from 47.9 μV/K in the as-deposited state to 97.3 μV/K. This improvement is attributed to a combination of factors, including the creation of energy-filtering grain boundaries, the presence of defect-induced localized states, and improved crystallinity. At 450 K, the post-annealed films exhibit a maximum thermoelectric power factor of 26.8 μW cm⁻¹ K⁻², reflecting a favorable balance between electrical conductivity and thermopower. Structural analysis via XRD and SEM confirms the formation of Ag₂Te secondary phases and grain boundaries through post-annealing, which collectively contribute to enhanced carrier mobility and energy filtering. These findings demonstrate that controlled post-annealing not only tailors the microstructure but also optimizes the carrier transport mechanisms in AgSnTe₂ thin films, highlighting their promise for mid-temperature thermoelectric energy conversion applications.