T. Muto, K. Kato, W. Morita
Keywords: thermoelectric generator, energy harvesting, flexible, waste heat recovery
Summary:Seebeck type thermoelectric (TE) generators are one of the promising devices for the waste heat conversion to the electricity as well as the energy harvesters at a temperature range between room temperature and 200 oC. The heat-to-electricity conversion efficiency of the TE generators is reached to 10 % at the TE figure of merit (ZT ) of 1. As a class of power generating devices, the TE generator lacks mechanical motion part unlike to the reciprocating electric generators. From this feature, the devices are suitable for miniaturization of the sizes, especially reduced thickness, and anticipated to the maintenance free behavior for the long time use. In our former report, we introduced TE ink material suitable for printing production of the TE materials. These materials are based on bismuth telluride (Bi2Te3) compounds and some additives, and the printed materials post thermal annealing showed ZT of 0.7 and 0.4 using the p- and n-type thermoelectric semiconductors, respectively. In this paper, we describe prototype production of a sheet-like TE generator using the ink materials and the sheet substrate having patterned metal electrodes. The formation of the TE layer was achieved by the conventional printed electronics (PE) processes [2,3]. By the use of the PE processes, the degree of freedom in designing the size and shape of our TE modules are improved. Actually, we obtained the short (few millimeters in the longest axis) and long (few 10 centimeters in length) modules with relevant substrates (Fig.1). The power generation performance of the generators was evaluated under the presence of controlled temperature differences, T. The power generation scale reached to W ~ mW order at a T less than 30 oC from a square module with a size of 75 x 75 mm2 (Fig.2). The plastic substrates, such as heat resisting polyimide films, are also applicable to the TE module platform. The use of the plastic substrates and an appropriate thermal design, the flexible TE modules have a total thickness of 0.4 mm were obtained. The flexible modules are bendable at an inward bending diameter of 30 mm, and the power generation performance was unchanged during the straight and bended states (Fig.3). From these features, the sheet-like TE generators described here are possible candidates for the energy harvester installable to the heat source surface have a versatile sizes (1 x 103~100 m), shapes, and dimensions. References:  M. Xie and D. M. Gruen, “Potential Impact of ZT = 4 Thermoelectric Materials on Solar Thermal Energy Conversion Technologies”, J. Phys. Chem. B, 2010, 114, 14339-14342.  K. Kato, T. Muto, T. Kondo, and K. Miyazaki, “Screen-printed sheet type thermoelectric module for power generation” (Oral Presentation). Material Research Society, Fall meeting, 2015, Boston.  Z. Cui, Printed Electronics: Materials, Technologies and Applications, John Wiley & Sons, 2016.