Improved thermoelectric performance of Ag2–xAlxSe through formation of AgAl phase

Abstract

Mixed ion–electron conductor Ag2Se is an n-type semiconductor owing to the intrinsic Se vacancies. By reducing Se vacancies, Ag2Se has been demonstrated as a potential environment-friendly thermoelectric material for near room temperature application. In the present work, Al addition was found to be highly beneficial for improving the thermoelectric properties of Ag2Se. In Ag1.95Al0.05Se, a large enhancement in the charge carrier mobility (1127 cm2/V s) is witnessed due to the formation of Se-rich Ag2Se1.02 phase with improved grain connectivity through in situ formed AgAl phase. The synergetic effect of low carrier concentration and enhanced mobility in Al doped samples resulted in a high Seebeck coefficient and high electrical conductivity, leading to a high power factor of 3039 μW/m K2 at 300 K. The figure-of-merit of Ag1.95Al0.05Se was found to be 1.1 at 300 K i.e., 57% higher than for pure Ag2Se. The uni-leg device fabricated using Ag1.95Al0.05Se with electroplated Ni/Ag contacts showed a conversion efficiency of ∼3.2% for a temperature difference of 93 K, i.e., comparable to the best reported value for conventional bismuth telluride.

Advances in Ag2Se-based thermoelectrics from materials to applications

“…164,229 Ahmad et al fabricated Ag 2 Se-based composites with in situ formed AgAI phases via a vacuum induction melting method. 116 A high μ of 1127 cm 2 V −1 s −1 can be obtained for Ag 1.95 AI 0.05 Se due to the optimized grain connectivity and reduced n , leading to a high S 2 σ of 30.39 μW cm −1 K −2 ; therefore an ultra-high room temperature ZT of 1.1 can be obtained at 300 K. 116 The rGO-Ag 2 Se composites were fabricated via a hydrothermal method with a subsequent hot-pressing technique. The 30wt% rGO-Ag 2 Se sample has a low κ of ∼0.492 W m −1 K −1 at 333 K, much lower than that of the other Ag 2 Se-based bulk materials.…”

“…141 Such a high value can even be competitive with Ag 2 Se-based bulk thermoelectric materials. 116,123…”

“…Ag 2 Se-AgAI composites, reproduced with permission. 116 Copyright 2022, AIP Publishing. Anisotropic film, reproduced with permission.…”

“…1(a) summarizes the temperature-dependent ZT values of Ag 2 Se-based bulk materials reported so far. Typical strategies for improving the ZT values of Ag 2 Se-based bulk materials include the introduction of a secondary phase (Ag 2 Se-0.5 wt% carbon nanotube (CNT), 112 Ag 2 Se-CuAgSe, 113 Ag 2 Se-5 mol% Te, 114 Ag 2 Se-AgSbSe 2 , 115 and Ag 2 Se-AgAI 116 ), alloying (Ag 2 Se 0.9 S 0.1 117 and Ag 2 Se 0.9 Te 0.1…”

“…1(a) summarizes the temperature-dependent ZT values of Ag 2 Se-based bulk materials reported so far. Typical strategies for improving the ZT values of Ag 2 Se-based bulk materials include the introduction of a secondary phase (Ag 2 Se–0.5 wt% carbon nanotube (CNT), 112 Ag 2 Se–CuAgSe, 113 Ag 2 Se–5 mol% Te, 114 Ag 2 Se–AgSbSe 2 , 115 and Ag 2 Se–AgAI 116 ), alloying (Ag 2 Se 0.9 S 0.1 117 and Ag 2 Se 0.9 Te 0.1 118 ), doping (Ag 2 Se doped by 1% Cu + 119 and Ag 1.9 Sn 0.1 Se 120 ), defect engineering (Ag 2 Se-hierarchical structure (HS) 121 and Ag 2 Se-liquid phase manipulation (LSM) 122 ), and stoichiometry manipulation (Ag 2 Se 1.015 , 123 Ag:Se = 2 ± 0.01, 124 and Ag 2 Se 1.01 125 ). Table 1 also summarizes the thermoelectric properties of Ag 2 Se-based bulk materials.…”