Thermo-optical Characterization of TPV selective emitters using ellipsometry.*

TPV systems convert heat to electricity via photons emitted from thermal emitters with spectra matched to photovoltaic cells. Optimizing conversion efficiency requires precise determination of the complex refractive index (n, k) of emitters at elevated temperatures. This work characterized the thermo-optical properties of thermal emitters from room temperature to 600°C to support optimization of thermophotovoltaic (TPV) efficiency at ultra-high operating conditions (~1800 °C). We established accurate room-temperature optical models of aluminum nitride (AlN) ceramic and silicon carbide (4H-SiC) from UV to NIR, as well as aluminum oxide on an aluminum nitride (Al₂O₃/AlN) thin film/substrate pair in the transparent region. Spectroscopic ellipsometry and WVASE modeling yielded mean square errors (MSE) of 1.239, 4.08, and 29.89, respectively, across a 240–2500 nm spectrum. Measurements were performed while heating samples from 25 °C to 600 °C. The extracted room-temperature properties were validated against literature values. We further observed temperature-dependent trends in optical properties that will guide future TPV emitter optimization.