The department develops materials, contacting techniques and system related aspects for thermoelectric generators (TEG) and sensors for applications in air and space, in vehicles and energy facilities at medium and high temperatures (250-1000°C). Specialised measurement equipment, amongst this several in-house developments, is used in national and international cooperations to characterize nanostructured thermoelectric high-temperature materials of novel substance classes with improved application properties and for tests of thermoelectric conversion modules. Uniquely within Germany the techniques available at DLR resemble a closed process chain from powder production to modules and their test in one location.
Thermoelectric Energy Conversion
Thermoelectric energy conversion, i.e. a direct conversion of thermal to electric energy in a solid, gains more and more technical importance for use of secondary energy in vehicles, for energy recovery from waste heat in industrial processes with high power consumption and for autonomous auxiliary power supplies. Developments within the department are aiming at promoting production technologies for materials and industrial scale joining processes. Besides a comprehensive system characterization of TEG modules activities include microanalytical investigations and mechanical tests of thermoelectric samples.
Novel Thermoelectric Materials
The targeted figure of thermoelectric materials´ developmetn is the thermoelectric efficiency. Thermoelectric materials with high thermoelectric efficiency allow for high energy conversion efficiencies, highest detectivity of sensors and best COP in Peltier-applications..
In the focus of application developments for TE energy conversion are materials for medium temperature ranges (above 250°C up to 500°C) based on tellurides, antimonides and silicides. Technology oriented material developments allowing potentially high through-puts of medium temperature materials that are with respect to applicability most advanced (mainly CoSb3-Skutterudites and Silicides) show increasing importance. Besides high efficiencies developments are targeting long-term functional stability at high operating temperatures.
Thermoelectric measurement technology
Combining unique in-house developments for measurements of Seebeck-Coefficient, electrical and thermal conductivities with characterizations of efficiencies of thermoelectric conversion modules DLR´s thermoelectric characterization lab disposes a one-of-a-kind infrastructure.
Reliable measurement set-ups for simultaneous temperature dependent evaluation of thermoelectric material and system properties are complex facilities whose operation relies on long-lived experience. The department conducts design, construction, instrumentation, process control development and test of modular automated measurement systems of thermoelectric quantities inclusing the thermoelectric Figure of Merit and local homogeneity of thermoelectric properties with micrometer resolution. A unique absolute method charcterizes with high accuracy the temperature dependent efficiency of thermoelectric generators under realistic variable thermal operating conditions and the sensitivity of high-temperature heat current sensors.
Thermoelectric sensors for usage at high temperatures based on active thermoelectric materials of high sensitivity show good linearity and functional long-term stability. In the center of developments are high-temperature stable contacts between sensor material and signal wire as well as thermomechanically stable composites of supporting structures, semi-conductor and cover layer. Adapted calibration and test facilities are developed for system evaluation. The department works on these aspects in the context of the development of a layer-structured linearized heat current sensor based on semi-conducting iron disilicide.