Optimized Thermoelectric Properties of Sulfide Compound Bi2SeS2 by Iodine Doping

Abstract

The Te-free compound Bi2SeS2 is considered as a potential thermoelectric material with less environmentally hazardous composition. Herein, the effect of iodine (I) substitution on its thermoelectric transport properties was studied. The electrical conductivity was enhanced due to the increased carrier concentration caused by the carrier provided defect Ise. Thus, an enhanced power factor over 690 μWm−1K−2 was obtained at 300 K by combining a moderate Seebeck coefficient above 150 µV/K due to its large effective mass, which indicated iodine was an effective n-type dopant for Bi2SeS2. Furthermore, a large drop in the lattice thermal conductivity was observed due to the enhanced phonon scattering caused by nanoprecipitates, which resulted in a low total thermal conductivity (<0.95 Wm−1K−1) for all doped samples. Consequently, a maximum ZT value of 0.56 was achieved at 773 K for a Bi2Se1−xIxS2 (x = 1.1%) sample, a nearly threefold improvement compared to the undoped sample.

Strain‐Mediated Lattice Rotation Design for Enhancing Thermoelectric Performance in Bi2S2Se

“…As a result, an ultra-high maximum figure-of-merit ZT max = 1.13 at 773 K (where ZT is equal to 0.21 for pristine Bi 2 S 2 Se at 773 K) with a high average figure of-merit (ZT ave ) = 0.54 (at 323-773 K) are realized, as shown in Figure 5f and Figure S17 (Supporting Information). The largest ZT obtained here is the record highest ZT reported in n-type Bi 2 S 2 Se mid-temperature range thermoelectric materials [29][30][31][32][33][34][35][36][37][38][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] (as shown in Figure S17, Supporting Information). Figure S18 (Supporting Information) shows the reproducibility of our high-performance thermoelectric sample.…”

“…That is sensible considering that the lattice parameters (a & c) of Sb 2 S 3 phase are smaller than those of Bi 2 S 2 Se 0.90 Cl 0.10 : fSb matrix, and when Sb 2 S 3 particle joins with Bi 2 S 2 Se 0.90 Cl 0.10 : fSb ) Schematic illustration of strain-induced lattice rotation in co-doped Bi 2 S 2 Se system; c) Sb doping dependent induced strain values and reduction in κ L in the present system; d) strain analysis mapping along e xx direction (calculated from the inset STEM micrograph), here color bar shows the distribution of strain in nanoprecipitates and matrix; e) a high resolution TEM micrograph showing interface between the Bi 2 S 2 Se 0.90 Cl 0.10 :fSb matrix and Sb 2 S 3 nanoprecipitates, where lattice difference can be observed; f) a schematic diagram to show the lattice variation between the embedded compressive nanophase experiencing an intensive force effect due to strained matrix (here inset [1] shows Inverse Fast Fourier Transform (IFFT) image of enlarged area indicating by yellow rectangle in (e) & [2] depicts a presentation of enlarged dislocation with the state of compression and extension at the interfaces due to dislocation); f) Electronic band structure for pristine (without strain) and Sb/Cl doped system under strain (0.4%); g) Schematic of band structure variation under Sb doping; h) the difference between the strain dependent reduction in κ s and nanoprecipitates dependendent reduction on reducing κ s i) comparison of ZT max between our Bi 2 S 2 Se 0.90 Cl 0.10 (f = 0.10) and recently reported literature. [29][30][31][32][33][34][35][36][37][38] matrix through interface tensile stress is produced at interfaces, leading to tensile strains in Sb 2 S 3 particles; signifying that the corresponding coherent and defect free lattice at interfaces between the matrix and nanophase (Figure S7b-g, Supporting Information). After Sb intercalation, the lattice parameters indicate crystal expansion due to Sb interlayer interactions (Figures S3 and S4, Supporting Information), which causes to induce strain in the matrix.…”

“…The largest PF of ≈7.18 µW cm −1 K −2 (at 773 K) is realized for Bi 2 S 2 Se 0.90 Cl 0.10 : f Sb ( f = 0.10), which the highest value than that of previously reported Bi 2 S 2 Se 1 and Bi 2 S 3 ‐based materials. [ 29–38,40–54 ]…”

“…a,b) Schematic illustration of strain‐induced lattice rotation in co‐doped Bi 2 S 2 Se system; c) Sb doping dependent induced strain values and reduction in κ L in the present system; d) strain analysis mapping along e xx direction (calculated from the inset STEM micrograph), here color bar shows the distribution of strain in nanoprecipitates and matrix; e) a high resolution TEM micrograph showing interface between the Bi 2 S 2 Se 0.90 Cl 0.10 : f Sb matrix and Sb 2 S 3 nanoprecipitates, where lattice difference can be observed; f) a schematic diagram to show the lattice variation between the embedded compressive nanophase experiencing an intensive force effect due to strained matrix (here inset [1] shows Inverse Fast Fourier Transform (IFFT) image of enlarged area indicating by yellow rectangle in (e) & [2] depicts a presentation of enlarged dislocation with the state of compression and extension at the interfaces due to dislocation); f) Electronic band structure for pristine (without strain) and Sb/Cl doped system under strain (0.4%); g) Schematic of band structure variation under Sb doping; h) the difference between the strain dependent reduction in κ s and nanoprecipitates dependendent reduction on reducing κ s i) comparison of ZT max between our Bi 2 S 2 Se 0.90 Cl 0.10 ( f = 0.10) and recently reported literature. [ 29–38 ] …”

“…The largest PF of ≈7.18 µW cm −1 K −2 (at 773 K) is realized for Bi 2 S 2 Se 0.90 Cl 0.10 : fSb (f = 0.10), which the highest value than that of previously reported Bi 2 S 2 Se 1 and Bi 2 S 3 -based materials. [29][30][31][32][33][34][35][36][37][38][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] The doping-dependent evolution in band structures of the Bi 2 S 2 Se, Cl-doped Bi 2 S 2 Se 1 and Sb-doped Bi 2 S 2 Se 1-x Cl x systems is depicted in Figure 4 and Figures S12, S13 (Supporting Information). The direct bandgap in pristine Bi 2 S 2 Se was evaluated to be 1.15 eV, which is consistent with the reported values.…”