Porous carbon-titania nanocomposite films for spectrally solar selective absorbers

Selective solar absorbers based on composition of porous titania and carbon with a well-defined interconnected macropores structure have been fabricated by a photopolymerization-induced phase-separation method in the framework of a sol-gel technique. Scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, thermogravimetric and differential thermal analysis, Fourier transform infrared spectroscopy, and spectroscopic ellipsometry were used to characterize the C-TiO2 films. The results showed that the macroporous structures of the films could be tuned by changing the reaction parameters. The reduction of the HNO3 concentration in the solution effectively decreases the mean size of pores, carbon content, and the thickness of the nanocomposite films, leading to an optimization of the spectral selective absorption performance. The solar absorptance (α) and thermal emittance (ε) of the optimized single layer film with a thickness of about 300 nm were about 0.95 and 0.12, respectively. The films also show good stability under the high temperature (~500 °C). Based on these results, porous carbon-titania composite films proved to be a good candidate as solar selective absorbers.