Medium-temperature thermoelectric GeTe: vacancy suppression and band structure engineering leading to high performance

Abstract

Achieving high electronic mobility and excellent thermoelectric performance in GeTe through Ge vacancy suppression and band structure engineering.

Positive Effect of Ge Vacancies on Facilitating Band Convergence and Suppressing Bipolar Transport in GeTe‐Based Alloys for High Thermoelectric Performance

“…The average ZT of the Ge 0.8 Pb 0.1 Bi 0.1 Te 1+ x within 300–773 K shows an increase trend with the amount of extra Te x (Figure 8b), increased by ≈94% from 0.69 for x = 0 to 1.34 for x = 0.06. Compared with previous reported GeTe‐based alloys, [ 21,24,26,33,40,42,43 ] our GeTe‐based alloys demonstrate superior thermoelectric ZT in both low‐ and high‐temperature region (Figure 8c), thus displaying outstanding average ZT within 300–773 K (Figure 8d).…”

“…The smaller values of Δ E L−H in the actual Ge 0.8 Pb 0.1 Bi 0.1 Te 1+ x should be ascribed to the extra contributions of band convergence from the other elements of Bi and Pb, which has also been suggested by other reports. [ 19,24,26 ]…”

“…Comparison of the c) temperature‐dependent ZT and d) average ZT of this work with other reported GeTe‐based alloys. [ 21,24,26,33,40,42,43 ]…”

“…Like other mid‐temperature thermoelectric materials (such as PbTe, [ 10,13 ] PbSe, [ 14 ] SnTe, [ 15 ] and SnSe [ 16,17 ] ), GeTe‐based alloys have also received great attention recently, [ 18–27 ] due to their special multiple‐band structures, relative low thermal conductivity and high carrier mobility. Ge vacancies can be easily formed in GeTe due to their low formation energy, [ 19,28 ] which lead to high hole concentration (≈10 21 cm −3 ), high κ e and therefore low ZT in un‐doped GeTe.…”

“…Many studies have considered Ge vacancies as negative effects for enhancing ZT of GeTe‐based alloys, [ 24,42,44,53–56 ] and have also proposed various approaches for suppressing Ge vacancies. Dong et al have reported that excess Ge can be effective in eliminating the Ge vacancies in pristine GeTe for reducing carrier density and increasing carrier mobility, [ 24 ] resulting in a peak ZT of ≈1.6 around 650 K. As reported by Li et al, [ 53 ] alloying with PbSe can elevate the formation energy of Ge vacancies by increasing the mean size of cations and decreasing the average size of anions, resulting in suppressed Ge vacancies. Bayikadi et al have shown that Ge‐vacancy level can also be decreased by proper heat treatment, resulting in a peak ZT of ≈1.37 in pristine GeTe.…”