Analysis of a high-efficiency tungsten nanobrick photonic crystal emitter for thermophotovoltaic systems

We demonstrate a 2D photonic crystal (PhC) selective emitter composed of tungsten nanobricks for broadband thermophotovoltaic (TPV) applications, achieving competitive efficiency at elevated temperatures. An optimization-based analysis is first employed to determine the optimal emissivity profile that maximizes conversion efficiency. The radiative properties of the emitter are then rigorously evaluated by considering contributions from both transverse electric (TE) and transverse magnetic (TM) polarized modes. To enable direct comparison with prior work, the efficiency of the proposed structure is calculated using three typical methodologies reported in the literature. Our analysis reveals that relying solely on normal emissivity can lead to significant (≈28%) overestimation of system performance, highlighting the importance of angular-averaged evaluation. Both protected and non-protected emitter configurations are investigated: the non-protected (protected) emitter achieves peak efficiencies of 56.7% (58.3%) at 1400K under normal emission conditions, while angular-averaged analysis reduces these values to 40.8% and 42.8%, respectively. The non-protected emitter exhibits substantial efficiency degradation during short-term operation due to oxidation and surface diffusion, whereas the protected configuration maintains 98% of its initial efficiency after 20 hours of continuous operation.