Tungsten-Carbon Nanotube Composite Photonic Crystals as Thermally Stable Spectral-Selective Absorbers and Emitters for Thermophotovoltaics

Thermophotovoltaics (TPVs) is a promising energy conversion technology which can harvest wide-spectrum thermal radiation. However, the manufacturing complexity and thermal instability of the nanophotonic absorber and emitter, which are key components of TPV devices, significantly limit their scalability and practical deployment. Here, tungsten-carbon nanotube (W-CNT) composite photonic crystals (PhCs) exhibiting outstanding spectral and angular selectivity of photon absorbance and thermal emission are presented. The W-CNT PhCs are fabricated by nanoscale holographic interferometry-based patterning of a thin-film catalyst, modulated chemical vapor deposition synthesis of high-density CNT forest nanostructures, and infiltration of the CNT forests with tungsten via atomic layer deposition. Owing to their highly stable structure and composition, the W-CNT PhCs exhibit negligible degradation of optical properties after annealing for 168 hours at 1273 K, which exceeds all previously reported high-temperature PhCs. Using the measured spectral properties of the W-CNT PhCs, the system efficiency of a GaSb-based solar TPV (STPV) that surpasses the Shockley-Queisser efficiency limit at modest operating temperatures and input powers is numerically predicted. These findings encourage further practical development of STPVs, and this scalable fabrication method for composite nanostructures could find other applications in electromagnetic metamaterials.