Boosting the thermoelectric performance of Bi₂O₂Se by isovalent doping

Abstract

N‐type Bi2O2Se has a bright prospect for mid‐temperature thermoelectric applications on account of the intrinsically low thermal conductivity. However, the low carrier concentration of Bi2O2Se (~1015 cm−3) severely limits its thermoelectric performance. Herein, the boosting of the carrier concentration to ~1019 cm−3 can be realized in our La‐doped Bi2O2Se ceramic samples, which could be ascribed to the formation of isoelectronic traps and the narrowing of band gap, and contribute to a marked increase in the electrical conductivity (from 0.03 S cm−1 to 182 S cm−1). Our X‐ray absorption near‐edge structure spectra results reveal that a local disordering of oxygen atoms could be an important reason for the intrinsically low thermal conductivity of Bi2O2Se, and the point defects can also suppress the lattice thermal conductivity in La‐doped Bi2O2Se. The ZT value can be enhanced by a factor of ~4.5 to 0.35 at 823 K for Bi1.98La0.02O2Se as compared to the pristine Bi2O2Se. The coordinated optimization of electrical and thermal properties demonstrates an effective method for the rational design of high‐performance thermoelectric materials.

Synchrotron X‐Ray Absorption Spectroscopy and Electrochemical Study of Bi2O2Se Electrode for Lithium‐/Potassium‐Ion Storage

“…As reported, there are two types of crystal structure with the same I4/mmm space group for tetragonal Bi 2 O 2 Se, whose structural discrepancy lies in the O atom position as was shown in Figure 4e,f, which makes it difficult to be distinguished by using XRD. [26] As shown in Figure S4a,b, Supporting Information, the experimental data fits well with the simulated model both in R space and k space, indicating the robust structural model based on structure type II. In contrary, the other fit model based on structure type I was rejected with a considerable large R-factor.…”

Infrared and Raman spectra of Bi2O2X and Bi2OX2 (X = S, Se, and Te) studied from first principles calculations

“…First, Bi 2 O 2 Se was suggested to be a good thermoelectric material. [2][3][4][5][6][7] In 2010, Ruleova et al reported the thermoelectric properties of Bi 2 O 2 Se and they found that Bi 2 O 2 Se is an n-type semiconductor with a very low thermal conductivity and a relatively high gure of merit ZT about 0.2 at 800 K. 2 Several theoretical works were also conducted to explore its thermoelectric properties. [8][9][10][11] Second, Bi 2 O 2 Se has an ultrahigh electron mobility.…”

Defects Engineering with Multiple Dimensions in Thermoelectric Materials

“…For the low electronegativity dopant atoms, the ability to attract holes is stronger, which facilitates the formation of a hole bound state, triggering the excitation of electrons and increasing the concentration of electrons. In contrast, the high electronegativity dopant atoms will form an electron bound state which increases the concentration of holes [32,33]. shown in Figure 3(b), the carrier concentration of pristine Bi 2 O 2 Se (shown in brackets) is only 1:55 × 10 15 cm -3 indicating the characteristics of insulators.…”

“…After La doping, the carrier concentration is boosted up to~10 19 cm -3 corresponding to the characteristic of a degenerate semiconductor, which contributes to the significant enhancement in electrical conductivity from 0.03 Scm -1 to 182 Scm -1 . Profited from the boosted electrical conductivity, the ZT value of Bi 2−x La x O 2 Se is significantly enhanced, which shows the feasibility of inducing isoelectronic trap to optimize carrier concentration and ZT value [33].…”

“…From another intuitive point of view, the point defects cause charge imbalance, inducing extrinsic carriers which change the electric transport properties. As for isoelectronic doping, although the chemical valence seems to be in balance, owing to the difference of electronegativity and atomic radius, the dopants can form an isoelectron trap [32][33][34][35][36] or alter the dominance of distinct types of point defects, both of which have an impact on the electrical properties. From the perspective of reciprocal lattice, the defects change the electronic and phonon structures which determine the intrinsic electrical and thermal transport properties.…”