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Bigger and Better Perovskite Solar Cells

Perovskite solar cells of more than 1 square centimeter have an average efficiency of 19.6%

2 min read
Perovskite solar cells made with vacuum-flash that surpass 20% efficiency.
Perovskite solar cells made with vacuum-flash that surpass 20% efficiency.
Photo: Alain Herzog/EPFL

Solar cells based on crystals known as perovskites have advanced by leaps and bounds in recent years. Now scientists have found a way to increase perovskite solar cell size while maintaining the device’s high conversion efficiencies.

In the span of less than a decade, the conversion efficiency of perovskite solar cells has grown from 3.8 to 22.1 percent, an unprecedented rise in the field of photovoltaics. Such devices are also appealing because they are much cheaper to make than the silicon wafers used in conventional solar cells.

However, a major drawback of high-efficiency perovskite solar cells is how small they generally are, ranging from 0.04 to 0.2 square centimeters. Currently, the best conversion efficiency of a perovskite solar cell larger than 1 square centimeter is 15.6 percent.

imgDescription: EPFL Professor Michael Graetzel holds a perovskite solar cell made with a vacuum-flash and which surpasses 20% efficiency.Photo: Alain Herzog/EPFL

Now scientists have created perovskite solar cells more than 1 square centimeter in size with an average conversion efficiency of 19.6 percent and a maximum efficiency of 20.5 percent, matching the performance of conventional thin-film solar cells of similar sizes.

"We have achieved an unprecedented efficiency level at a larger size, which has been a problem so far," says study co-author Michael Grätzel, director of the Swiss Federal Institute of Technology Lausanne's Laboratory of Photonics and Interfaces. "How high can we go with efficiency? Theoretical efficiencies are around 30 percent. While we might not get to theoretical efficiencies, we can still go much higher than we have currently."

Conventional manufacturing techniques for perovskite solar cells precipitate solid perovskites from a solution by dripping a chemical known as an "anti-solvent" into the center of the perovskite film as it is spun. However, this results in blotchy impurities and ultimately leads to defects in the perovskite film. In addition, the anti-solvents currently used are toxic and harmful to the environment, hampering their large-scale application, Grätzel says.

Instead, the researchers employed an anti-solvent-free technique called vacuum-flash solution processing. This new technique uses a few seconds of mild vacuum to dry up solvent and help trigger precipitation of solid perovskite. In combination with rapid heat annealing, this method resulted in thin, smooth, highly oriented crystalline perovskite films.

"We can very simply get remarkable results compared to anti-solvent methods," Grätzel says. "We are now excited about scaling up to make bigger modules."

The scientists detailed their findings online June 9 in the journal Science.

The Conversation (0)
This photograph shows a car with the words “We Drive Solar” on the door, connected to a charging station. A windmill can be seen in the background.

The Dutch city of Utrecht is embracing vehicle-to-grid technology, an example of which is shown here—an EV connected to a bidirectional charger. The historic Rijn en Zon windmill provides a fitting background for this scene.

We Drive Solar

Hundreds of charging stations for electric vehicles dot Utrecht’s urban landscape in the Netherlands like little electric mushrooms. Unlike those you may have grown accustomed to seeing, many of these stations don’t just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Debates over the feasibility and value of such vehicle-to-grid technology go back decades. Those arguments are not yet settled. But big automakers like Volkswagen, Nissan, and Hyundai have moved to produce the kinds of cars that can use such bidirectional chargers—alongside similar vehicle-to-home technology, whereby your car can power your house, say, during a blackout, as promoted by Ford with its new F-150 Lightning. Given the rapid uptake of electric vehicles, many people are thinking hard about how to make the best use of all that rolling battery power.

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