How efficient are thermoelectric materials? – An assessment of state-of-the-art individual and segmented thermoelectric materials

Abstract

To efficiently convert heat into electricity using thermoelectric energy harvesting, it is essential to employ new material strategies. One effective approach is segmentation, where compatible materials optimized for different operating temperatures are combined to improve thermoelectric efficiency. Despite reports of severe efficiency reductions when segmenting incompatible materials, an updated assessment of the compatibility across state-of-the-art thermoelectric materials is missing. Here, we employ a numerical model to assess how efficiently non-segmented and segmented high-performing thermoelectric materials can convert heat into electricity. For the non-segmented materials, efficiency reaches up 17.9% at ΔT = 615 K without heat losses and contact resistances. Losses due to self-incompatibility were generally found to be small for most materials (<0.6% points) with few exceptions. In contrast, segmented thermoelectric legs were very sensitive to compatibility effects. Segmentation is found to only boost the efficiency significantly for ΔT > 300 K. Here, we find efficiencies of up to 24% for p-type AgSb0.94Cd0.06Te2/Pb0.98Te0.02-8%SrTe and 19% for n-type Bi1.8Sb0.2Te2.7Se0.3/Pb0.93Sb0.05S0.5Se0.5. We further map out the maximum tolerable contact resistances before segmentation becomes detrimental. By providing an overview of the achievable energy conversion efficiencies, this study highlights the present state of thermoelectric energy conversion and critically assesses the prospects of segmentation.