Reduced bipolar conduction in bandgap-engineered n-type Cu0.008Bi2(Te,Se)3 by sulfur doping

Weon Ho Shin, Hyun Sik Kim, Se Yun Kim, Sung sil Choo, Seok won Hong, Yeseong Oh, Yerim Yang, Yoona Kim, Hee Jung Park, Sang il Kim

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

Significant bipolar conduction of the carriers in Bi2Te3-based alloys occurs at high temperatures due to their narrow bandgaps. Therefore, at high temperatures, their Seebeck coefficients decrease, the bipolar thermal conductivities rapidly increase, and the thermoelectric figure of merit, zT, rapidly decreases. In this study, band modification of n-type Cu0.008Bi2(Te,Se)3 alloys by sulfur (S) doping, which could widen the bandgap, is investigated regarding carrier transport properties and bipolar thermal conductivity. The increase in bandgap by S doping is demonstrated by the Goldsmid–Sharp estimation. The bipolar conduction reduction is shown in the carrier transport characteristics and thermal conductivity. In addition, S doping induces an additional point-defect scattering of phonons, which decreases the lattice thermal conductivity. Thus, the total thermal conductivity of the S-doped sample is reduced. Despite the reduced power factor due to the unfavorable change in the conduction band, zT at high temperatures is increased by S doping with simultaneous reductions in bipolar and lattice thermal conductivity.

Original languageEnglish
Article number337
JournalEnergies
Volume13
Issue number2
DOIs
StatePublished - 2020

Keywords

  • Bandgap
  • Bipolar conduction
  • Point defect
  • S doping
  • Thermoelectric

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