Liquid-Phase Manipulation Securing Enhanced Thermoelectric Performance of Ag₂Se

Abstract

Developing n-type materials with high peak and/or average ZT (ZT is the figure of merit) is an urgent need for the lower ZT of the existing n-type BiTeSe materials compared with the p-type BiSbTe materials. Here, we demonstrate that liquid-phase sintering can lead to lowered thermal conductivity and an improved power factor in n-type Ag2Se, which originates from the greatly lowered electronic thermal conductivity attributed to the decreased mobility and improved Seebeck coefficients because of increased effective mass. Benefiting from this, the maximum ZT (ZTmax) of ∼1.21 and the average ZT (ZTave) of 1.06 are successfully achieved in polycrystalline Ag2Se. In this work, ZTave is the highest reported value, being 26% larger than that of Ag2Se reported. Our work shows that liquid-phase sintering to achieve improved thermoelectric (TE) performance opens a great opportunity for designing prospective thermoelectrics.

Thermoelectric Ag2Se: Imperfection, Homogeneity, and Reproducibility

“…It is obvious that a slight increase in Se content can effectively enhance the zT of Ag 2 Se 1+ x while excess Ag deteriorates TE performance. As shown in Figures and f, the maximum average zT can be improved to 0.8–0.9 over 300–380 K for Se-rich compositions, which is among the highest values for Ag 2 Se-based materials. ,− The decent performance was obtained by virtue of two aspects. On the one hand, the synthesis method, particularly the M + SPS method, yields high-quality samples.…”

“…The bottleneck for these Mg-containing materials is the inferior stability due to the high chemical activity of Mg and the difficulty in synthesis. , Ag 2 Se, an eco-friendly and low-cost n-type semiconductor, can be another choice. Ag 2 Se shows high carrier mobility (∼1500 cm 2 /V s), low thermal conductivity (∼1.3 W/mK), and decent zT values (see Figure ) at room temperature. − …”

“…Herein, M, MA, and SPS are the abbreviations of melting, mechanical alloying, and spark plasma sintering, respectively. (1–14) Physical methods include 1: M; 2: zone melting; 3: liquid-phase manipulation based on M; 4: M (this work); 5: M + SPS; 6: M + SPS; 7: M + SPS (this work); 8: MA + SPS; 9: MA + SPS (this work); 10: dissociative adsorption reaction + SPS; 11: dissociative adsorption reaction + cold pressing; 12: self-propagating high-temperature synthesis + hot pressing; 13: manual mixing + SPS; and 14: mixed powder + cold pressing . (15–18) Chemical methods include 15: wet chemical synthesis + SPS; 16: hydrothermal reaction + SPS; 17: colloidal synthesis + hot pressing; and 18: aqueous solution synthesis + SPS …”

“…Various methods have been developed to synthesize Ag 2 Se bulk materials but have yielded noticeably different thermoelectric properties. Figure summarizes the highest zT values of Ag 2 Se 1+ x prepared by various methods. ,− The zT values at room temperature range from 0.37 (wet chemical synthesis + SPS, No. 15) to 0.92 (liquid-phase manipulation based on melting, No.…”

Ag2Se/nylon self-supporting composite films for wearable photo-thermoelectric generators with high output characteristics

“…15,19 For now, the optimization of Ag 2 Se is mainly achieved by doping, 20 and tuning the stoichiometric ratio 21,22 and the synthesis process 17,23 to improve its RT TE performance, and most of the related studies are focused on bulk materials. Although the energy conversion efficiency of bulk Ag 2 Se is already at the leading position in the eld of thermoelectricity (ZT value close to 1), 16,24,25 the exibility of TE materials is also necessary to provide the required comfort (wearable electronics) and to better cover heat sources for higher energy conversion efficiency. [26][27][28][29][30] Flexible TE lms are currently divided into two main categories: non-self-supporting and self-supporting lms, of which the former have exible substrates at the top or bottom to confer exibility to the composites.…”