Low cost thin film power generator fabricated by screen print technique

Abstract

Recently, energy harvesting is main issue all over the world due to limited energy source and an increasing population. Thermoelectric module is one of the possible solutions to get green energy. Thermoelectric module can convert waste heat into electrical energy. Moreover, it can be used as a cooler if the electrical energy is supplied [1]. However, its application is limited due to its low efficiency and quite high price. In cooler, if the efficiency is low, the module consumes lots of electric power source. It can increase running cost, so high efficiency is crucial in cooler. But in power generator, even though the efficiency is low, we can add lots of thermoelectric module to get a lot of electrical power. As a result, low cost thin film power generator is focused in this research. $Bi_2Te_3$ is widely used as a thermoelectric material, but it is toxic and quite expensive. Zn-Sb was chosen as a thermoelectric material, it is nontoxic and cheaper than $Bi_2Te_3$. Moreover, if the module is fabricated by screen printing technique, soldering process, that is necessary if bulk type is used, is not need. It decreases labor cost. Finally, the screen printing technique is very fast, very simple and low cost technique, so it is suitable for mass production. In this way, we can effectively reduce manufacturing cost of TE module. In this work, Zn-Sb films were deposited by screen printing technique and evaluated its properties. The films were porous, but its thermoelectric properties were comparable to those of bulk type. Zn percent and annealing temperature were varied. It was verified that annealing temperature should be below $500^\circC$ and 50% ~ 60% of Zn percent was preferable. Finally, two types of TE modules, which is planar type and vertical type, were made by screen printing technique and their output powers were measured. It is around 0.17mW/$cm^2$ ~ 0.3mW/$cm^2$, when the temperature difference is 50K. Each type has its own advantages and disad...