This paper considers a range of techniques which – within the realm of classical optics – can be used to enhance light capture as a first step in photovoltaic energy conversion. Examples include a simple case of downshifting, fluorescent collectors which reduce the size of a light beam, and a novel form of light trapping to increase the path length of light within the solar cell. The results are discussed using a thermodynamic framework where the energy exchange with an absorbing/fluorescent medium allows the entropy of the captured photon gas to be lowered, reducing the étendue of the emitted beam. We show that frequency management represents a powerful tool, allowing enhancement in light trapping above the Yablononovitch limit, leading to potentially highly efficient but very thin crystalline silicon solar cells.

The integrity and reliability of surface protective coatings deposited on metal surface could be in-situ monitored via the attractive luminescence sensing technique. In this paper, we report the influence of substrate temperature on the properties of erbium (Er) doped aluminum nitride (AlN) film, which could be applied as a luminescent layer for monitoring the health of multilayered Al/AlN coating. The AlN:Er films were deposited via reactive radio-frequency magnetron sputtering, and the silicon substrate temperature was varied from non-intentional heating up to 400 °C. The composition, morphology, crystalline structure, and dielectric function of the AlN:Er films deposited under these different substrate temperature conditions were studied. These properties of the AlN:Er films show strong correlation with the substrate temperature maintained during film fabrication. The obtained AlN:Er films, without further annealing, exhibited photoluminescence peaks of the Er³⁺ ions in the visible wavelength range and the strongest photoluminescence intensity was observed for the AlN:Er film deposited with the temperature of substrate kept at 300 °C. The results demonstrated in this work offer guidance to optimize the substrate temperature for the deposition of AlN:Er film for future application of this sensing technique to thin metal components.