A Promising Selective Emitter Ho(Ta1-xNbx)O4 with Enhanced Performance for Thermophotovoltaic Applications

Selective emitters with high spectral efficiency and structural stability are essential for efficient thermophotovoltaic systems. However, achieving simultaneous spectral matching and simplified fabrication remains a significant challenge. In this study, a series of selective emitters Ho(Ta1-xNbx)O4 were prepared via the straightforward solid-state reaction of Ho2O3 and Ta2O5. First-principles calculations were performed in order to further tune the electronic structure and optical bandgap of HoTaO4. Experimental results revealed that Nb5+ induced lattice distortion and symmetry reduction, effectively narrowing the bandgap and enhancing the Ho3+ 4f-4f electronic transitions. The optimized emitter exhibited a spectral efficiency of 47.59% at 1573 K, a peak power density of 9.65 W cm-2, and a figure of merit of 28.02% when paired with InGaAsSb cells (1.8-2.5 μm). Furthermore, the emitters demonstrated reduced thermal conductivity (3.74 W m-1 K-1) and suppressed grain growth (kp = 0.0451 μm2 h-1), ensuring excellent microstructural stability under extreme thermal conditions. This work provides a strategy for designing high-performance selective emitters for advanced energy conversion and industrial waste heat recovery.