Spectrum-tailorable two-dimensional silicon–titanium nitride selective emitter by photon recycling for thermophotovoltaic applications

Thermophotovoltaic (TPV) systems have gained attention for their ability to convert radiant energy from heat sources into electricity. One major challenge is fabricating a spectrum-tailorable selective emitter with high performance at elevated temperatures. In this study, two-dimensional (2D) silicon-titanium nitride (Si–TiN) photonic crystals (PhCs) with TiN-coated Si cavities were fabricated using nanosphere lithography (NSL). The lossy nature and high reflectivity of TiN in the long-wavelength range allow the Si–TiN PhC to achieve up to $\sim$92% broadband optical emissivity (200 nm – cut-off wavelength) while minimizing heat radiation to $\sim$27% in the long-wavelength range (5 – 10$\mu m$). More importantly, thanks to the isotropy of the NSL method based on oxygen plasma etching (OPE), different periods and radius of the Si–TiN PhC can be achieved by controlling the OPE time or the initial polystyrene sphere diameter. This enables precise control over the cut-off wavelength and emission spectrum to match various PV cells. The 2D Si–TiN PhC produced 3.13 times more power than a flat Si emitter. This approach provides a promising path forward for enhancing TPV system performance and practical applications.