Maximizing the thermoelectric performance of topological insulator Bi2Te3 films in the few-quintuple layer regime

Using first-principles calculations and the Boltzmann theory, we explore the feasibility to maximize the thermoelectric figure of merit (ZT) of topological insulator Bi2Te3 films in the few-quintuple layer regime. We discover that the delicate competitions between the surface and bulk contributions, coupled with the overall quantum size effects, lead to a novel and generic non-monotonous dependence of ZT on the film thickness. In particular, when the system crosses into the topologically non-trivial regime upon increasing the film thickness, the much longer surface relaxation time associated with the robust nature of the topological surface states results in a maximal ZT value, which can be further optimized to similar to 2.0 under physically realistic conditions. We also reveal the appealing potential of bridging the long-standing ZT asymmetry of p-and n-type Bi2Te3 systems.