近赤外太陽光熱電発電のためのマイクロフレネルレンズの作製

抄録

Energy harvesting devices that convert ambient energies such as light, thermal, and vibration energies into the order of microwatts have been required for sensors in Internet of Things society. In previous research, we have demonstrated flexible thermoelectric devices that transmit visible light. The device converted near-infrared solar light by generating temperature gradient using micro-ball lenses However, the flexibility of the device was low due to their thick ball lenses. In this study, thinfilm thermoelectric devices with micro-Fresnel lenses were fabricated. Each micro-Fresnel lens with the height of 15 μm and the diameter of 1 mm was designed and fabricated using lithography and imprint processes. A photoresist Mold I was formed using femtosecond laser internal writing, and then transferred to a polydimethylsiloxane flexible Mold II. Finally, a microFresnel lens of epoxy resin was fabricated using Mold II. The diameter of the focal spot was approximately 172 μm when the solar light (AM 1.5) was vertically irradiated to the micro-Fresnel lens. Solar concentration was approximately 33 times. When the micro-Fresnel lenses were fabricated onto the thin-film thermoelectric device, the open-circuit voltage of 38 μV and the maximum power of 0.47 nW were successfully generated by the solar light. The generation properties were estimated to be 1.17 V/m² and 18.7 μW/m² that were almost the same values obtained by the previous device using ball lenses although the thickness of the device enabled to be reduced by 59%.