Researchers at the University of Michigan in the US developed colour-neutral transparent solar cells that set a new efficiency record of 8.1% efficiency with 43.3% transparency.

The new solar cells bring us a step closer to skyscrapers that serve as power sources. Rather than conventional silicon, the cells are organic, or carbon-based, because this offers a combination of very high efficiency and very high visible transparency.

The new material is a combination of organic molecules engineered to be transparent in the visible and absorbing in the near infrared, an invisible part of the spectrum that accounts for much of the energy in sunlight. In addition, the researchers developed optical coatings to boost both power generated from infrared light and transparency in the visible range—two qualities that are usually in competition with one another.

The solar cells were made in two variations, a colour-neutral one that has the effect of a car window, and an even more efficient one of 10.8% with 45.8% transparency. This effect is created by adding a silver electrode instead of an indium tin oxide of the colour neutral version. However, the latter has a green tint that may not be acceptable in some window applications.

Previous transparent solar cells have light utilization efficiencies of roughly two to three percent, but the indium tin oxide cell is rated at 3.5% and the silver version has a light utilization efficiency of 5%.

Both versions can be manufactured at large scale, using materials that are less toxic than other transparent solar cells.

Photos: Robert Coelius / Michigan Engineering Communications & Marketing