Toward tiny high-power-density thermoelectric harvesters

Thermoelectric (TE) generators (TEGs) have recently attracted significant attention for harvesting ubiquitous heat energy to power industrial sensor nodes or wearable and implantable electronics. Such applications require that a small, fitted heat sink be incorporated into a tiny harvester to ensure conformal deployment and ease of use. Since the small heat sink will exhibit very poor heat rejection performance, the optimal structural design of the TEG device and the proper selection of its constituent TE materials are extremely important to ensure that sufficient electric power is provided to the connected post-stage circuits. Regrettably, the traditional forward design strategies, i.e., material-to-device and device-to-harvester, are often disconnected from one another and fail to form a complete chain, thereby presenting a fundamental challenge in achieving ultrahigh-power-density harvesters. Here we present a zero-dimensional model for a tiny harvester to establish a set of new metrics (not limited to the figure of merit zT) that can be used to determine the optimal TE material and to directly deduce the optimal configuration of the TEG for guaranteeing the maximum output power at various load conditions, making backward design strategy possible. Two tiny harvesters are accordingly fabricated and exhibit areal power densities 52 and 94 times that of a harvester incorporating a commercial TEG, with identical amounts of TE material used for each.