Solar cell breakthrough hints at how windows could one day be power hubs

Windows that generate household energy are a step closer to becoming a reality for UK homes after a team of scientists made a technological breakthrough: a higher efficiency transparent solar cell.

Tesla has already launched new solar roof panel technology that resembles standard roof tiles, and these transparent solar cells mark another step towards the exterior of our homes becoming green power generators. 

And the combination of the two could potential provide 100% of the power to our homes one day, researchers at Michigan State University even claim.

While transparent solar panels already exist, these new transparent solar cells could be the boost it needs to become mainstream technology. It could then be installed in windows, greenhouses, glass façades, and potentially also consumer electronics like tablets and phones, the researchers claim.

Here's everything you need to know about the transparent solar cell technology.

What are the new transparent solar cells?

A team from École Polytechnique Fédérale de Lausanne in Switzerland made a breakthrough in the efficiency of a type of solar cell called a DSC that is transparent. 

The transparent solar cell, which is not currently used in 'standard' solar panels used in the UK due to its inefficiency, harvests light from the entire spectrum using photosensitizer dye molecules.

Mesoscopic dye-sensitised solar cells (DSCs) convert light into electricity through photosensitizers — formed of dye compounds that absorb light and inject electrons into an array of oxide nanocrystals, which are then collected as electric current.

The cells generate electric power by moving electrons from the photosensitiser towards an electrical output like a device or a storage unit.

However, while they are already being used in skylights, greenhouses, as well as glass facades, such as those adorning the SwissTech Convention Center, their previous inefficiency has so far given them limited application. (A total of 355 see-through panels have already been installed at the SwissTech Convention Center in Lausanne, Switzerland, and generate a respectable 2,000kWh.)

With this breakthrough, this could now be about to change.

How do these solar cells differ to 'regular' solar panels?

DSCs solar cells were invented in 1990s by scientist Brian O'Regan and Michael Grätzel, an EPFL professor, taking on the latter’s name — Grätzel cells.

However, their inefficiency meant their commercial usage was limited, with preference instead going to the crystalline silicon solar cells used in most solar PV panels.

Now scientists from the groups of Grätzel and Anders Hagfeldt at École Polytechnique Fédérale de Lausanne have developed a way of improving the packing of two new photosensitizer dye molecules to enhance the DSC’s photovoltaic performance.

Using the new technique, the team was able to develop DSCs with a power conversion efficiency of 15.2% for the first time under standard global simulated sunlight, with long-term operational stability tested over 500 hours.

By increasing the active area to 2.8 cm2, the power conversion efficiency spanned 28.4% – 30.2% over a wide range of ambient light intensities along with outstanding stability.

The authors write: “Our findings pave the way for facile access to high performance DSCs and offer promising prospects for applications as power supply and battery replacement for low-power electronic devices that use ambient light as their energy source.”

With solar panel glass, the solar-harvesting system converts sunlight into electricity. However, the DSCs are unique in that they let visible light pass through while picking up just the invisible wavelengths of sunlight in the ultraviolet and the near-infrared to convert into renewable electricity.

Once installed, the panels are visibly indistinguishable from traditional windows.

Could the technology be used to power smartphones?

Smartphones and other consumer technologies could one day be powered by invisible solar panels incorporated into the device’s screen. It would mean the user could charge the phone using the power of the sun while out and about.

Last year it was reported how a team from Incheon National University in South Korea have suggested that either titanium dioxide or nickel oxide could be used to capture light and convert it into an electrical current to power a phone.

Professor Joondong Kim and his colleagues say titanium oxide production is able to absorb invisible ultraviolet light while letting visible light range pass through it, while nickel oxide, similarly has a high optical transparency.

More than half of all visible light passed through the cell, giving it a transparent effect, with a power conversion efficiency of 2.1% which is high when you consider the technology only targets a small part of the light spectrum in order to remain invisible.

"While this innovative solar cell is still very much in its infancy, our results strongly suggest that further improvement is possible for transparent photovoltaics by optimizing the cell's optical and electrical properties," Professor Kim said.