ALD-Based Interface Engineering for Improving Electrical Conductivity of Nanoporous Thermoelectric Materials

Abstract

The way to improve the performance of thermoelectric materials is to break the strong correlation between electrical conductivity and thermal conductivity. Combining porous structures with atomic layer deposition (ALD) is a promising strategy to solve this problem. The porous structure introduced into thermoelectric materials effectively lowers the lattice thermal conductivity, greatly increasing performance. However, the formation of nanopores is accompanied by a decrease in electrical conductivity. Here, we create nanoporous Bi0.4Sb1.6Te3 powder formed through selective dissolution from the mixture of KCl and Bi0.4Sb1.6Te3 powder. We propose a strategy to control carrier concentration by ALD of ZnO on nanoporous Bi0.4Sb1.6Te3 powder, thereby improving electrical conductivity and lowering thermal conductivity. Even after spark plasma sintering, ZnO is conformally formed at the nanoporous Bi0.4Sb1.6Te3 grain boundaries. The electrical conductivity increases from 651.72 S/cm to 724.52 S/cm by interfacial reaction of ZnO and Bi0.4Sb1.6Te3. In addition, ZnO inhibits grain growth and creates numerous grain boundaries to lower the lattice thermal conductivity of the porous structure. As a result, the ZT of the nanoporous Bi0.4Sb1.6Te3 deposited with ZnO is increased by 46%. This study demonstrates that ALD is an effective method for improving the conductivity of nanoporous thermoelectric materials.