Ana Frias

High-Performance Near-Infrared Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) appear as candidates to enhance the performance of photovoltaic (PV) cells and contribute to reduce the size of PV systems, decreasing, therefore, the amount of material needed and thus the cost associated with energy conversion. One way to maximize the device performance is to explore near-infrared (NIR)-emitting centers, resonant with the maximum optical response of the most common Si-based PV cells. Nevertheless, very few examples in the literature demonstrate the feasibility of fabricating LSCs emitting in the NIR region. In this work, NIR-emitting LSCs are reported using silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) (SiNc or NIR775) immobilized in an organic-inorganic tri-ureasil matrix (t-U(5000)). The photophysical properties of the SiNc dye incorporated into the tri-ureasil host closely resembled those of SiNc in tetrahydrofuran solution (an absolute emission quantum yield of ∼0.17 and a fluorescence lifetime of ∼3.6 ns). The LSC coupled to a Si-based PV device revealed an optical conversion efficiency of ∼1.5%, which is among the largest values known in the literature for NIR-emitting LSCs. The LSCs were posteriorly coupled to a Si-based commercial PV cell, and the synergy between the t-U(5000) and SiNc molecules enabled an effective increase in the external quantum efficiency of PV cells, exceeding 20% in the SiNc absorption region.

Liquid Hydrostatic Pressure Optical Sensor Based on Micro-Cavity Produced by the Catastrophic Fuse Effect

We propose an optical fiber hydrostatic pressure sensor based on micro-cavities generated by the fiber fuse effect. The presented sensor is manufactured through the recycling of optical fiber destroyed by the fiber fuse effect, being, therefore, a cost-effective solution, when compared with other similar micro-cavity-based solutions. The developed sensor was characterized for pressures up to 20 kPa, showing a linear sensitivity coefficient of 0.47 ± 0.03 nm · kPa-1, for pressure values below 8 kPa. Furthermore, we propose a new theoretical model to describe the behavior of the microcavities embedded in optical fibers. This allows us to solve the discrepancies, already identified by other authors, between the experimental results and the ones attained with the flat mirrors Fabry-Perot model. By this way, we were able to describe the sensor response, within the full dynamic range.

Sustainable luminescent solar concentrators based on organic–inorganic hybrids modified with chlorophyll

Luminescent solar concentrators (LSCs) are luminescent waveguide layers that convert sunlight into specific wavelengths which are then guided by total internal reflection to a PV device located at the edges of the LSC. Their ability to concentrate sunlight onto small areas makes LSCs a useful complement to silicon-based PVs in a series of applications, such as urban integration and flexible fabrics towards mobile solar-energy. Challenges for the luminescent layer include the use of low-cost and sustainable nature-based organic molecules. We report novel chlorophyll-based LSCs with emission properties in the red/NIR spectral region. Here, chlorophyll molecules extracted from Spirulina maxima, an abundant cyanobacterium and an attractive natural source, are immobilized in organic–inorganic di- and tri-ureasil matrices enabling the production of sustainable LSCs. At low chlorophyll concentrations (<3 × 1017 molecules per cm3), the photophysical properties of the chlorophyll molecules after incorporation into the hybrids closely resemble those in ethanolic solution (with an absolute emission quantum yield of ∼0.16 and a fluorescence lifetime of ∼8 ns). The LSCs were coupled to a Si-based commercial PV device revealing optical conversion efficiency and power conversion efficiency values of ∼3.70% and 0.10%, respectively, illustrating the potential of this approach for the development of nature-based LSCs meeting the requirements of reliable, sustainable and competitive energy systems.

Evaluation of the fuse effect propagation velocity in bend loss insensitive fibers

In this work we investigate the dynamics of the fuse effect propagation in bend loss insensitive fibers. The fuse velocity, threshold power and void period values were compared with those obtained for standard single mode fibers. The results show that the power dependent optical discharge velocity coefficient is 32% higher in G.657 fibers than that in G.652 fibers.

Sensors based on recycled optical fibers destroyed by the catastrophic fuse effect

In the last decades the fiber Bragg gratings (FBG) and Fabry-Perot Interferometer (FPI) micro cavities based sensors have become one of the most attractive optical fiber sensing technologies. However, its production requires a significant economical investment. We propose a cost effective solution based on micro cavity generated by the recycling of optical fibers destroyed through the catastrophic fuse effect. This technique considerably reduces the experimental complexity and the production costs. In this paper, the application of these sensors in the monitoring of several parameters, such as refractive index, pressure, strain and temperature is presented.

Evaluation of the temperature increase on the fiber fuse effect end point

In this work we compare the thermal behavior, in the fuse effect end point, of bend insensitive optical fiber (G.657) with the standard single mode fiber (G.652). We verify that the G.657 fibers display a higher average temperature value in the mentioned position, which can be explained by the shape of the final void.