Metal substrate boosts perovskite solar cells

Silicon, the standard semiconducting material used in a host of applications, including computer central processing units (CPUs), semiconductor chips, detectors and solar cells, is an abundant, naturally occurring material. However, it is expensive to mine and purify.

Perovskites – a family of materials named for their crystalline structure – have shown extraordinary promise in recent years as a far less expensive, equally efficient replacement for silicon in solar cells and detectors. Now, a team of researchers led by Chunlei Guo, a professor of optics at the University of Rochester, has proposed a simple way to make perovskites far more efficient.

Researchers typically synthesize perovskites in a wet lab, and then apply the material as a film on a glass substrate. Guo and his team propose a different approach. By using a substrate made up of either a layer of metal or alternating layers of metal and a dielectric material – rather than glass—he and his colleagues found they could increase the light-conversion efficiency of perovskite by 250%. They report their findings in a paper in Nature Photonics.

“No one else has come to this observation in perovskites,” Guo says. “All of a sudden, we can put a metal platform under a perovskite, utterly changing the interaction of the electrons within the perovskite. Thus, we use a physical method to engineer that interaction.”

Metals are probably the simplest materials in nature, but they can be made to acquire complex functions. The Guo Lab has extensive experience in this area. The lab has pioneered a range of technologies for transforming simple metals into pitch black, superhydrophilic (water-attracting) or superhydrophobic (water-repellent) materials. In their recent studies, they have used these enhanced metals for solar-energy absorption and water purification.

In this latest paper, instead of presenting a way to enhance the metal itself, the Guo Lab demonstrates how to use the metal to enhance the efficiency of perovskites. “A piece of metal can do just as much work as complex chemical engineering in a wet lab,” says Guo, adding that this new research may be particularly useful for future solar-energy harvesting.

In a solar cell, photons from sunlight need to interact with and excite electrons, causing them to leave their host atoms and generate an electrical current. Ideally, the solar cell would use materials that are too weak to pull the excited electrons back to their host atoms and thus shut off the electrical current.

Guo’s lab demonstrated that such recombination could be substantially reduced by combining a perovskite material with either a layer of metal or a metamaterial consisting of alternating layers of silver and aluminum oxide, a dielectric.

The result was a significant reduction in electron recombination through “a lot of surprising physics”, Guo says. In effect, the metal layer serves as a mirror that creates reversed images of electron-hole pairs, weakening the ability of the electrons to recombine with the holes.

The lab was able to use a simple detector to observe the resulting 250% increase in the light-conversion efficiency.

Several challenges must be resolved before perovskites become practical for applications, especially their tendency to degrade relatively quickly. Currently, researchers are racing to find new, more stable perovskite materials.

“As new perovskites emerge, we can then use our physics-based method to further enhance their performance,” Guo says.

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