Abstract
High ZT of 1.34 at 766 K and a record high average ZT above 1 in the temperature range of 300-864 K are attained in n-type PbTe by engineering the temperature-dependent carrier concentration and weakening electron–phonon coupling upon Ga doping. The experimental studies and first principles band structure calculations show that doping with Ga introduces a shallow level impurity contributing extrinsic carriers and imparts a deeper impurity level that ionizes at higher temperatures. This adjusts the carrier concentration closer to the temperature-dependent optimum and thus maximizes the power factor in a wide temperature range. The maximum power factor of 35 µW cm−1 K−2 is achieved for the Pb0.98Ga0.02Te compound, and is maintained over 20 µWcm−1 K−2 from 300 to 767 K. Band structure calculations and X-ray photoelectron spectroscopy corroborate the amphoteric role of Ga in PbTe as the origin of shallow and deep levels. Additionally, Ga doping weakens the electron–phonon coupling, leading to high carrier mobilities in excess of 1200 cm2 V−1 s−1. Enhanced point defect phonon scattering yields a reduced lattice thermal conductivity. This work provides a new avenue, beyond the conventional shallow level doping, for further improving the average ZT in thermoelectric materials.
Original language | English (US) |
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Article number | 1800659 |
Journal | Advanced Energy Materials |
Volume | 8 |
Issue number | 21 |
DOIs | |
State | Published - Jul 25 2018 |
Funding
The authors wish to acknowledge support from the Natural Science Foundation of China (Grant Nos. 51521001, and 51632006). At Northwestern University (X.S., S.H., C.W., and M.G.K.), synthesis, thermoelectric property measurements and band structure calculations were supported by a grant from the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences under Award No. DE-SC0014520.
Keywords
- Ga doping
- PbTe
- deep level impurities
- thermoelectric properties
ASJC Scopus subject areas
- Renewable Energy, Sustainability and the Environment
- General Materials Science