Ag2Se is a narrow band gap n-type semiconductor with high carrier mobility and low lattice thermal conductivity. It has high thermoelectric performance near room temperature. However, there is a noticeable data discrepancy for thermoelectric performance in the reported literature studies, which greatly hinders the rational understanding and potential application of this material. In this work, we comprehensively studied the homogeneity, reproducibility, and thermal stability of bulk Ag2Se prepared by melting and mechanical alloying methods followed by spark plasma sintering. By virtue of the atom probe topology technique, we revealed nanosized Ag- or Se-rich precipitates and micropores with Se-aggregated interfaces that have not been detected previously. The samples prepared by melting and spark plasma sintering exhibit the best homogeneity and repeatability in thermoelectric properties despite abundant nanoprecipitates. Moreover, the thermoelectric performance of Ag2Se is greatly improved by introducing a slight amount of excess selenium. The average zT can steadily reach 0.8–0.9 in the range of 300–380 K, which is among the highest values reported for Ag2Se-based materials. This work will rationalize the evaluation of the thermoelectric performance of Ag2Se.

Flexible electronics ushers in a revolution to the electronics industry in the 21st century. Ideally, all components of a flexible electronic device including the functional component shall comply with the deformation to ensure the structural and functional integrity, imposing a pressing need for developing roomtemperature strain-tolerant semiconductors. To this end, there is a long-standing material dilemma: inorganic semiconductors are typically brittle at room temperature except for size-induced flexibility; by contrast, organic semiconductors are intrinsically soft and flexible but the electrical performance is poor. This is why the discovery of bulk plasticity in Ag 2 S at room temperature and ZnS in darkness is groundbreaking in solving this long-standing material dilemma between the mechanical deformability and the electrical performance. The present review summarizes the background knowledge and latest advances in the emerging field of plastic inorganic semiconductors. At the outset, we argue that the plasticity of inorganic semiconductors is vital to strain tolerance of electronic devices, which has not been adequately emphasized. The mechanisms of plasticity are illustrated from the perspective of chemical bonding and dislocations. Plastic inorganic materials, for example, ionic crystals (insulators), ZnS in darkness, and Ag 2 S, are discussed in detail in terms of their prominent mechanical properties and potential applications. We conclude the article with several key scientific and technological questions to address in the future study.

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