Energy-harvesting from low-temperature environmental heat via thermoelectric generators (TEG) is a versatile and maintenance-free solution for large-scale waste heat recovery and supplying renewable energy to a growing number of devices in the Internet of Things (IoT) that require an independent wireless power supply. A prerequisite for market competitiveness, however, is the cost-effective and scalable manufacturing of these TEGs. Our approach is to print the devices using printable thermoelectric polymers and composite materials. We present a mass-producible potentially low-cost fully screen printed flexible origami TEG. Through a unique two-step folding technique, we produce a mechanically stable 3D cuboidal device from a 2D layout printed on a thin flexible substrate using thermoelectric inks based on PEDOT nanowires and a TiS2:Hexylamine-complex material. We realize a device architecture with a high thermocouple density of 190 per cm² by using the thin substrate as electrical insulation between the thermoelectric elements resulting in a high-power output of 47.8 µWcm−² from a 30 K temperature difference. The device properties are adjustable via the print layout, specifically, the thermal impedance of the TEGs can be tuned over several orders of magnitudes allowing thermal impedance matching to any given heat source. We demonstrate a wireless energy-harvesting application by powering an autonomous weather sensor comprising a Bluetooth module and a power management system.
Light extraction from organic light emitting diodes (OLEDs) is attracting considerable interest as being crucial for enhancing the energy efficiency in lighting applications. Light extraction can be realized by lithographically defined internal diffraction gratings or stochastic scattering centers. The former approach needs in addition an external optical layer for scrambling the angularly dependent emission spectra in order to avoid color shifts [1]. Micro lens arrays cannot only be used for fulfilling this task but they can also be used for enhancing the luminosity into a specific direction. We demonstrate recent advances towards high efficiency OLEDs with high directionality. In addition to the relevant technologies we have also developed a comprehensive simulation software for the quantitative description of the light propagation inside the devices. Here, a particular challenging task is the description of multiple and coherent optical scattering. We have recently developed a software for the exact simulation based on a scattering matrix formalism [2].[1] T.
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