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 Al2O3 layer over n-type Bi2Te2.7Se0.3 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 Al2O3 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-Al2O3 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 Al2O3 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 Al2O3 coating with a single ALD cycle. Our approach offers new insights into the simultaneous reduction of the κ and electron concentration in n-type Bi2Te3-based materials.