Device optimization and large-scale roll-to-roll manufacturability of flexible thin-film thermoelectric generators

The optimization of flexible thin-film thermoelectric generators (TEGs) suitable for large-area roll-to-roll (R2R) processing is investigated. The selection of suitable contact materials, in-line patterning of connections, and dimension of the thermoelectric (TE) strip are studied. As a result, copper is selected for contacts because it possesses a similar performance to gold while being cheaper. Both in-series- and in-parallel-connected devices are found to work well and provide a voltage-dominant and current-dominant power source, respectively. The Seebeck coefficient and internal resistance of a device are extracted from the fit line to the measured power data. The in-parallel-connected TEG has a much smaller internal resistance and is thus suitable for wearable/portable devices with a small load resistance. A shorter and wider TE strip generates more power. To the authors’ knowledge, this is the first study that experimentally proves a downward trend of power output with increasing strip length. In addition, an industrially feasible/continuous process is proposed for large-scale manufacture of flexible TEGs, by R2R sputtering TE materials on polymer webs, inkjet printing contacts, and segmenting using a laser. A segmented configuration is able to relieve internal strains in the device, while subjected to bending (e.g., within a wristband) to retain performance.