Researchers from the University of Minnesota and the University of Milano-Bicocca have been working in collaboration to bring the concept of windows that can efficiently collect solar energy to a reality. They now believe they are only a short distance away from realizing their goal, thanks to high-tech silicon nanoparticles. 
The researchers have managed to create a technology that embeds the silicon nanoparticles into an efficient luminescent solar concentrator (LSCs). The LSCs are the most important part of the window to enable the efficient capture of solar energy. When light shines through the surface, the common frequencies of light are trapped inside and directed towards the edges, where smaller solar cells are put into a position to capture the energy. 
Windows that can collect solar energy, called photovoltaic windows, are the next frontier in renewable energy technologies, as they have the potential to largely increase the surface of buildings suitable for energy generation without impacting their aesthetics -- a crucial aspect, especially in metropolitan areas. LSC-based photovoltaic windows do not require any bulky structure to be applied onto their surface and since the photovoltaic cells are hidden in the window frame, they blend invisibly into the built environment.

The idea of solar concentrators and solar cells integrated into building design has been around for decades, but this study included one key difference -- silicon nanoparticles. Until recently, the best results had been achieved using relatively complex nanostructures based either on potentially toxic elements, such as cadmium or lead, or on rare substances like indium, which is already massively utilized for other technologies. Silicon is abundant in the environment and non-toxic. It also works more efficiently by absorbing light at different wavelengths than it emits. However, silicon in its conventional bulk form, does not emit light or luminesce.

"In our lab, we 'trick' nature by shirking the dimension of silicon crystals to a few nanometers, that is about one ten-thousandths of the diameter of human hair," said University of Minnesota mechanical engineering professor Uwe Kortshagen, inventor of the process for creating silicon nanoparticles and one of the senior authors of the study. "At this size, silicon's properties change and it becomes an efficient light emitter, with the important property not to re-absorb its own luminescence. This is the key feature that makes silicon nanoparticles ideally suited for LSC applications."
"Over the last few years, the LSC technology has experienced rapid acceleration, thanks also to pioneering studies conducted in Italy, but finding suitable materials for harvesting and concentrating solar light was still an open challenge," said Sergio Brovelli, physics professor at the University of Milano-Bicocca, co-author of the study, and co-founder of the spin-off company Glass to Power that is industrializing LSCs for photovoltaic windows "Now, it is possible to replace these elements with silicon nanoparticles."
The University of Minnesota invented the process for creating silicon nanoparticles about a dozen years ago and holds a number of patents on this technology. In 2015, Kortshagen met Brovelli, who is an expert in LSC fabrication and had already demonstrated various successful approaches to efficient LSCs based on other nanoparticle systems. The potential of silicon nanoparticles for this technology was immediately clear and the partnership was born. The University of Minnesota produced the particles and researchers in Italy fabricated the LSCs by embedding them in polymers through an industrial based method, and it worked.
"This was truly a partnership where we gathered the best researchers in their fields to make an old idea truly successful," Kortshagen said. "We had the expertise in making the silicon nanoparticles and our partners in Milano had expertise in fabricating the luminescent concentrators. When it all came together, we knew we had something special."
Funding for the research study includes a grant from the U.S. Department of Energy (DOE) Office of Basic Science Center for Advanced Solar Photophysics, an Energy Frontier Research Center and a grant from the European Community's Seventh Framework Programme. Ehrenberg also received funding from a National Science Foundation (NSF) Fellowship and the Benjamin Y.H. and Helen Liu Fellowship.
Source: ScienceDaily, 2017