Optical emitters for thermophotovoltaics: from photonics to thermochemical stability

Thermophotovoltaics (TPV) represent a promising route for converting heat generated as a byproduct into usable electricity through a clean energy paradigm. However, the material options used to date for the optical emitters substantially constrain the power conversion efficiency of this process. Specifically, we focused our search to dual-layer emitters that could be achieved in thin-film or patterned forms. Thus, we screened the optical response (i.e. permittivity) of >2,800 material combinations with melting point >2,000 oC, The mismatch in permittivity allowed for emission control, key for the development of high performing TPV. We found a handful of emitters for TPV with theoretical efficiency >60% at 1800 oC, for GaSb solar cells. To complement our analysis, we also identified optimal material combinations for InGaAsSb, InGaAs, Ge, GaSb, and Si solar cells. The final down selection of materials is also based on their thermal expansion and thermochemical stability, which are frequently overlooked. We also quantify the response of B4C/AlN using in situ, high-temperature optical measurements.