Enhanced thermoelectric properties of Mn Cu1.8S via tuning band structure and scattering multiscale phonons

Enhanced Thermoelectric Performance of Bi–Se Co-Doped Cu1.8S via Carrier Concentration Regulation and Multiscale Phonon Scattering

“…The optical band gap ( E g ) was evaluated from the plot hv dependence of ( ahv ) 2 with extrapolating a straight line to ( ahv ) 2 = 0 as shown in Figure a, where v , h , and a denote the light frequency, Planck constant, and absorption coefficient, respectively. Cu 1.8 S obtained an E g of 1.69 eV, which is close to the reported 1.69–1.71 eV. , Further increasing x to 0.03 produces a monotonically decreased E g to 1.57 eV for the Cu 1.8–2 x Bi 2 x S 1–3 x Se 3 x samples. Figure b shows the schematic diagram for the band structure change.…”

“…Cu 1.8 S obtained an E g of 1.69 eV, which is close to the reported 1.69−1.71 eV. 33,36 Further increasing x to 0.03 produces a monotonically decreased E g to 1.57 eV for the Cu 1.8−2x Bi 2x S 1−3x Se 3x samples. Figure 4b shows the schematic diagram for the band structure change.…”

“…Moreover, these Cu-rich phases and point defects are the original factors to phonon scattering, resulting in a decreased κ l . Besides, the reduced μ is related to the increased DOS effective mass ( m d * ) obtained from the Pisarenko plot between the α and n shown in Figure b, in which m d * was calculated according to a single parabolic band (SPB) model described in eqs –, , with an acoustic phonon-dominated scattering mechanism. where η is the reduced Fermi energy, F n (η) is the n -th order Fermi integral, r is the scattering factor, and k B is the Boltzmann constant. It is shown in Figure b that the estimated m d * at room temperature slightly increases from 2.4 m e to 3.8 m e after introducing Bi and Se, indicating an adjusted band structure for Bi–Se co-doped Cu 1.8 S alloys.…”

“…The maximum conversion efficiency (η max ) was calculated by ZT eng and PF eng considering the Thomson heat under a large temperature difference, as shown in Figure a,b, and the detailed equations are described in the Supporting Information. , A ZT eng of ∼0.16 was obtained in the temperature range of 323–773 K for the x = 0.03 bulk and its derived η max reaches up to ∼3.50%, exhibiting a notable promotion compared with x = 0 (η max ∼ 1.89%). The TE properties of the Cu 1.8 S compound can be further enhanced via co-doping at both the cation site and the anion site or compositing high-valence metal compounds to regulate Cu vacancies’ concentration, together with other strategies such as nanostructure engineering, band engineering, and entropy engineering.…”

“…26,27 Excessive Cu vacancies result in a higher n, which is detrimental to TE performance. 28 At present, multiple strategies have been used to promote the TE properties of Cu 1.8 S, including element doping with Sb, 29 Pb, 30 Bi, 31 Ti, 32 Mn, 33 Na, 34 In, 35 Te, 36 Sb-Sn, 37 and rare-earth trichlorides 38 to adjust n for enhancing α, as well as compositing with SiC, 39 Bi 2 S 3 , 40 WSe 2 , 41 and SiO 2 42 to reduce κ. Ge et al 38 directly introduced 2 wt % LaCl 3 into Cu 1.8 S, which effectively enhanced α due to both the reduced n and enhanced DOS, leading to an optimized PF of 1600 μW•m −1 • K −2 at 773 K. Qin et al 39 obtained refined grains by dispersing SiO 2 nanoparticles in Cu 1.8 S, which significantly scattered phonons and reduced κ from 1.98 W m −1 K −1 for Cu 1.8 S to 0.7 W m −1 K −1 for 1 wt % SiC-dispersed Cu 1.8 S bulk at 773 K. In addition, some novel strategies were also used to improve the TE properties in other Cu−S binary systems. Liu et al 43 optimized the Cu vacancy concentration and reduced the phase transition temperature in Cu 2−x S using a solvothermal method, leading to an improved PF and a higher ZT avg ∼ 0.76 (T = 573−833 K).…”