Lanthanide-based downshifting layers tested in a solar car race


The mismatch between the AM1.5G spectrum and the photovoltaic (PV) cells absorption is one of the most limiting factors for PV cells performance. Typically, silicon-based PV devices present low performance in the UV spectral range and, thus, the UV component of solar radiation is wasted. One way to enhance this aspect and, consequently, increase PV cell’s overall efficiency, is through the use of luminescent layers which are placed on top of the PV device (as a coating), and are able to absorb the UV component of solar radiation and convert it to visible radiation, which will then efficiently used by the PV device. In this work, red and green emitting luminescent layers were tested in PV cells, resulting in a relative increase in the delivered power and an absolute increase of external quantum efficiency of 14% and 27%, respectively. Moreover, as a proof of context, these layerswere tested in PV cells attached to small solar vehicles. A solar powered car race was organized in which the vehicle containing the PV cells coated with the luminescent downshifting layers presented a relative increase in the velocity of 9%, when compared to that with the uncoated one. 


Scheme of the solar vehicle with (a) bare PV cell and (b) PV cell with the luminescent downshifting (LDS) layer and (c) photographs of the solar vehicles race (the circles surround the modified solar car). 

The research group of Prof. Rute A.S. Ferreira and Prof. Luís D. Carlos (CICECO – Aveiro Institute of Materials, University of Aveiro, Portugal) and of Prof. Paulo André (Instituto de Telecomunicações, University of Aveiro, Portugal) developed UV down shifting coatings for PV cells based on lanthanide-doped organic-inorganic hybrids to promote more efficient solar energy harvesting of silicon-based conventional PV cells. The layers are able to shape the incident sunlight to match the PV cells absorption. The electrical measurements on the PV cells performed before and after the deposition of the layers, confirm the positive effect of the coatings on the cell’s performance. The maximum delivered power and the maximum absolute external quantum efficiency increased 14% and 27%, respectively. Moreover, a solar powered car race was organized in which the vehicle containing the PV cells coated with the luminescent downshifting layers presented a relative increase in the velocity of 9%, when compared to that with the uncoated one. The results of this work prove the effectiveness of using luminescent materials as coating for PV devices with the goal of enhancing their performance.

About the Group
The Photonic Hybrids and Nanomaterials Group (Phantom-g), from University of Aveiro, Portugal, was pioneer in Europe in the study of organic-inorganic light emitting hybrids, namely embedding lanthanide centers. In the last decade, the group has established an international network devoting to these luminescent hybrid materials with more than 30 research groups in Spain, France, Italy, Germany, Poland, UK, Netherlands, China, Japan, Brazil and Australia. Several PhD students have performed joint thesis abroad in Spain, France and Brazil. Moreover, foreign PhD students from laboratories belonging to that cooperation network, from Poland, Brazil, UK, Austria, China, Spain, France and Italy, have performed part of their research in Aveiro. The research is organized in five main research lines: integrated optics, luminescent solar concentrators, solid-state lighting, nanothermometry and single-ion and single-molecule magnets. The research work of Phantom-g presents a strong experimental component, reason why the group is equipped with diverse facilities to perform the sample preparation and photophysical characterization, including fluorometers, hyperspectral microscope, spectroscopic ellipsometer, UV-Visible-NIR spectrometer, solar simulator and several integrating spheres for emission quantum yield (UV-Visible-NIR ranges) and luminous flux measurements.

Article
Correia S F H , Bastos A R N, Fu L S, Carlos L D, André P S et al. Lanthanide-based downshifting layers tested in a solar car race. Opto-Electron Adv 2, 190006 (2019).
DOI:10.29026/oea.2019.190006