In‐situ elemental reaction‐regulated Ag₂S films enable the best thermoelectric performances

Abstract

Silver sulfide thin film, with excellent thermoelectric properties, is few reported due to the complex and time‐consuming high‐temperature or high‐pressure synthesis process. Here, a fast ionic conductor n‐type Ag2S film with good crystallinity and uniform density is prepared by sputtering metal Ag films of different thicknesses on glass and then reacting in S precursor solution at low temperature. At 450 K, β‐Ag2S films can be obtained and underwent a phase transition from α‐Ag2S monoclinic, which had a significant effect on their electrical and thermal properties. The grain size of Ag2S films increases with the increase of film thickness. Before and after the phase transition, the carrier concentration and mobility cause obvious changes in the electrical properties of Ag2S. The carrier concentration of body‐centered cubic phase β‐Ag2S is about three orders of magnitude higher than that of monoclinic phase α‐Ag2S, and the mobility is also 2–3 times that of the latter. Especially, after the phase transition, the conductivity of β‐Ag2S rises exponentially from the zero conductivity of α‐Ag2S and increases with the increase of temperature. The Ag2S film shows the highest figure of merit of 0.83 ± 0.30 at 600 K from the sample with ∼1600 nm thickness, which is the highest record among Ag2S‐based thermoelectric materials reported so far.

Enhanced Thermoelectric Performance in Flexible Sulfur-Alloyed Ag2Se Thin Films

“…Moreover, the absence of diffraction peaks corresponding to other sulfur compounds in the XRD results further confirms that the S element has successfully substituted the Se element. 39 As depicted in Figure 1b, the c-axis orientation factor F (for detailed calculations, refer to the Supporting Information) decreases with increasing sulfur content, further proving the effect of sulfur on orientation. Nevertheless, the F value for all samples remains above 0.85, signifying that the film still maintains a c-axis preference (an F value of 1 indicates perfect orientation).…”

“…The lattice distortion induced by the excess anion sulfur might have an important influence on the orientation change of the sulfur-alloyed Ag 2 Se films, and similar tendency was also observed in Se-enriched and Cu-doped Ag 2 Se films. Moreover, the absence of diffraction peaks corresponding to other sulfur compounds in the XRD results further confirms that the S element has successfully substituted the Se element . As depicted in Figure b, the c -axis orientation factor F (for detailed calculations, refer to the Supporting Information) decreases with increasing sulfur content, further proving the effect of sulfur on orientation.…”