A special invisibility cloak guides sunlight past the contact fingers to the active surface area of the solar cell. Image: Martin Schumann, KIT.
A special invisibility cloak guides sunlight past the contact fingers to the active surface area of the solar cell. Image: Martin Schumann, KIT.

Scientists at the Karlsruhe Institute of Technology (KIT) have proposed an unconventional approach to increasing the light-harvesting efficiency of solar cells, which currently stands at around 20%. As detailed in Optica, they suggest using optical invisibility cloaks to guide sunlight around objects that cast a shadow on the solar cells.

The solar panels currently mounted on roofs convert just one fifth of the light they receive into electricity, which means that about 80% of the solar energy is lost. There are many reasons for these high losses, but an important one is that up to one-tenth of the surface area of the solar panel is covered by so-called contact fingers that extract the generated electric current. But these contact fingers partly block the incoming light, preventing it reaching the active area of the solar panel and thus reducing the panel’s efficiency.

"Our model experiments have shown that the cloak layer makes the contact fingers nearly completely invisible," says Martin Schumann from the KIT Institute of Applied Physics, who conducted the experiments and simulations. Together with scientists from various German universities and research institutes, physicists at KIT, led by project head Carsten Rockstuhl, modified an optical invisibility cloak previously designed at KIT so that it would guide the incident light around the contact fingers of a solar panel.

Normally, invisibility cloak research is aimed at making objects invisible; for this purpose, light is guided around the object to be hidden. This research project did not focus on hiding the contact fingers visually, but on guiding the light around them so that it could reach the active surface area of the solar cells.

To achieve this cloaking effect, the scientists propose applying a polymer coating onto the solar cells. This coating should possess finely calculated optical properties, meaning an index of refraction that varies according to location or special surface shapes, and should also be grooved along the contact fingers. In this way, the incident light should be refracted away from the contact fingers to reach the active surface area of the solar panel (see Image).

By means of a model experiment and detailed simulations, the scientists demonstrated that both coating concepts are suited for hiding the contact fingers. In the next step, they plan to apply the cloaking layer onto a solar cell in order to confirm the increase in efficiency. The physicists are optimistic that efficiency will be improved by the cloak under real conditions: "When applying such a coating onto a real solar cell, optical losses via the contact fingers are supposed to be reduced and efficiency is assumed to be increased by up to 10%," says Schumann.

This story is adapted from material from the Karlsruhe Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.