US and Italian researchers are another step forward in making energy harvesting windows a reality, thanks to a new breakthrough in silicon nanoparticle technology.

Energy harvesting windows work by capturing light on luminescent solar concentrators (LSCs), which then transport the useful frequencies to the glass’s edge, where photovoltaic cells wait to produce electricity.

Development of efficient, cost-effective LSCs and photovoltaic windows could be key to the transition to net zero commercial buildings, as the building-integrated technology increases enormously the amount of surface area solar energy can be harvested from. It is also done without impacting on aesthetics, as the photovoltaic cells are hidden in the window frame.

A recent Australian report named building-integrated photovoltaics as a key technology for commercial buildings to reach net zero, which was estimated to cost 1-1.15 per cent of construction costs.

While solar window technology has been on the cards for a while (see Transparent solar windows a step closer), the researchers from the University of Minnesota and University of Milano-Bicocca said their technology had a winning difference – silicon nanoparticles.

Formerly, the most efficient LSCs had been developed using relatively complex nanostructures based on toxic substances such as cadmium or lead, or rare substances such as indium.

The researchers said that as well as silicon being more abundant and non-toxic, it was also worked more efficiently by absorbing light at different wavelengths than it emits.

Light concentrated to the edge of the silicon-based luminescent solar concentrator

“In our lab, we ‘trick’ nature by shrinking the dimension of silicon crystals to a few nanometers, that is about one ten-thousandths of the diameter of human hair,” University of Minnesota mechanical engineering professor Uwe Kortshagen said.

“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.”

Co-author Sergio Brovelli from the University of Milano-Bicocca said while LSC technology had been developing rapidly, finding suitable materials for harvesting and concentrating solar light had been a challenge.

“Now, it is possible to replace these elements with silicon nanoparticles.”

The nanoparticle technology has the potential to capture more than five per cent of the sun’s energy at what the researchers said was “unprecedented” low costs.

“This will make LSC-based photovoltaic windows a real technology for the building-integrated photovoltaic market without the potential limitations of other classes of nanoparticles based on relatively rare materials,” co-author Francesco Meinardi said.

The research has been published in Nature Photonics.