Grain boundary engineering strategy for simultaneously reducing the electron concentration and lattice thermal conductivity in n-type Bi2Te2.7Se0.3-based thermoelectric materials.

This study demonstrates atomic layer deposition (ALD) of an extremely thin Al 2 O 3 layer over n-type Bi 2 Te 2.7 Se 0.3 to alleviate the adverse effects of multiple boundaries on their thermoelectric performance. Multiple boundaries reduce thermal conductivity (κ), but generate electrons, deviating from the optimum carrier concentration. Only one Al 2 O 3 ALD cycle effectively suppresses Te volatilization at the grain boundaries, resulting in a decrease from 5.8 × 1019/cm3 to 3.6 × 1019/cm3 in the electron concentration. Concurrently, the one-cycle-Al 2 O 3 coating produces fine grains, thus inducing numerous boundaries, ultimately suppressing the lattice κ from 0.64 to 0.33 W/m·K. A further increase in the number of Al 2 O 3 cycles leads in a significant rise in the resistance, resulting in degradation of thermoelectric performance. Consequently, the ZT value is increased by 51 % as a result of Al 2 O 3 coating with a single ALD cycle. Our approach offers new insights into the simultaneous reduction of the κ and electron concentration in n-type Bi 2 Te 3 -based materials. • Boundary engineering strategy for thermoelectric materials. • Conformal and thin Al 2 O 3 layer over n-type Bi 2 Te 2.7 Se 0.3 thermoelectric materials. • Facile atomic layer deposition-based approach. • Suppression of Te volatilization at the grain boundaries. • Simultaneous reduction of lattice thermal conductivity and electron concentration. [ABSTRACT FROM AUTHOR]