Enhanced Near-Room-Temperature Thermoelectric Properties in Yb-Doped Off-Stoichiometry α-Cu2+ x Se

Abstract

Cu2Se is a well-known high zT thermoelectric (TE) material, but at room temperature it has poor TE properties due to its excessive carrier concentration resulting from spontaneously formed Cu vacancies. Attempts at carrier concentration optimization or band structure modification by doping have not been as successful because most dopants have low saturation limits in Cu2Se and further lower the Cu vacancy formation energy, generating more vacancies that act as compensating dopants. We have found that by simultaneously adding excess Cu to suppress the formation of Cu vacancies and adding Yb dopants to modify the electronic band structure to enhance the Seebeck coefficient in Cu2+xSe, a zT value of 0.57 at 300 K can be obtained for Cu2.072Yb0.003Se. The enhanced Seebeck coefficient, combined with the low thermal conductivity, yields high zT values at room temperature, making it a potential alternative for energy harvesting applications. Our results show that simultaneously suppressing Cu vacancies by adding excess Cu and band structure modification by adding an impurity dopant can be an effective strategy in enhancing the RT TE properties of Cu2Se. This approach can also be effective in other Cu chalcogenide materials that are similarly plagued by excessive hole concentrations that result from Cu vacancies.