Increasing the efficiency of Luminescent Solar Concentrators by rational chemical design

In the past two decades lot of research has focused on Luminescent Solar Concentrators (LSC) as a way to reduce the costs of solar photovoltaics.1 LSC devices usually consist in a thin slab of transparent material (glass or polymer) doped with a fluorescent dye in which a fraction of the emitted radiation remain trapped inside the slab and can be then collected at the edges. Compared to traditional concentrators, which make use of mirrors and lenses, this kind of devices show numerous advantages like theoretical higher concentration factors,2 the ability to work with both diffuse and incident light3 and no need for tracking devices or cooling apparatuses.4 More than that, the simplicity and the low cost of this devices make them particularly appealing. Still, high efficiencies with low cost materials, which would make the success of this technology, have not been obtained yet.5 A simple approach to improve the performances of LSC devices can arise from a better understanding of the dye-polymer systems used. In particular we investigated the relation between the output efficiency and various LSC device parameters like the dye concentration and the polymer thickness for different commercial and synthetic dyes characterized by different spectroscopic features. This has been accomplished using a novel homebuilt experimental setup which allowed us to explore the different systems in a fast, sensible and reproducible way profiting the use of a photodiodic system. General trends were found for the different dye/polymers which could be related to the their spectroscopic characteristics. It will be then shown how the obtained data can be used to rethink the design of thin-layer devices by means of multi-coating layers and achieve an increase in the efficiency of about 6%. To increment further the output efficiency over the solar spectrum absorption properties, multi-dye systems were also investigated and an increase of 8% in power output was reported for energy-cascade LSC compared to single-dye thin film LSC. This study was supported by the Fondazione Pisa under “POLOPTEL” (project no. 167/09) and by MIUR-FIRB (RBFR122HFZ).