Dear colleagues and friends,
A dear colleague shares this article, written by Yvaine Ye, published on March 21, 2024 in the CU Boulder Today newsletter at the University of Colorado (CU) in Boulder and translated by us for this space. Let's see what it's about...
The world of solar energy is ready for a revolution. Scientists are rushing to develop a new type of solar cell using materials that can convert electricity more efficiently than current panels.
In an article published on February 26 in the journal Nature Energy, a researcher from the University of Colorado (CU) in Boulder and his international collaborators unveiled an innovative method for manufacturing new solar cells, known as perovskite cells, a fundamental achievement for the commercialization of what many consider to be the next generation of solar technology.
Today, almost all solar panels are made of silicon, which is 22% efficient. This means that silicon panels can only convert about a fifth of solar energy into electricity because the material absorbs only a limited proportion of the wavelengths of sunlight. Silicon production is also expensive and consumes a lot of energy.
Introducing Perovskite
The perovskite cell is partly made of synthetic material that has been modeled based on the special crystal structure of a mineral called perovskite. This structure absorbs sunlight in a different and more efficient way than silicon cells, meaning it has the potential to convert considerably more solar energy at a lower production cost.
Synthetic perovskite takes its name from the homonymous mineral, perovskite, which was first discovered in 1839 in the Ural Mountains by Gustav Rose and named in recognition of the Russian mineralogist L. A. Perovski (1792—1856).
And indeed, this new material has the same type of crystal structure as calcium titanate (CaTiO3), known as a perovskite structure.
“Perovskites could be a game changer,” said Michael McGehee, a professor in the Department of Chemical and Biological Engineering and a member of the UC Institute for Renewable and Sustainable Energy in Boulder.
Scientists have been testing perovskite solar cells by stacking them on top of traditional silicon cells to form tandem cells. Laying two materials in layers, each absorbing a different part of the solar spectrum, can potentially increase panels' efficiency by more than 50%.
“We're still seeing rapid electrification around the world, including a greater number of cars running on electricity. To slow the advance of climate change, we hope to retire more coal plants and eventually dispose of natural gas plants,” said McGehee. “If we believe that we are going to have a fully renewable future, then we must be planning for the wind and solar markets to expand at least five to ten times compared to what we are now. “
To achieve this, he said, the industry must improve the efficiency of solar cells.
But a major challenge in manufacturing them from perovskite on a commercial scale is the process of coating the semiconductor on the glass plates that are the basic components of the panels. Currently, the coating process has to be carried out in a small box filled with non-reactive gas, such as nitrogen, to prevent perovskites from reacting with oxygen, which decreases their performance.
“This is fine at the research stage, but when you start coating large pieces of glass, it becomes increasingly difficult to do so in a box filled with nitrogen,” McGehee said.
McGehee and his collaborators found a way to avoid that harmful reaction with air. They found that adding dimethylammonium formate, or DMAFO, to the perovskite solution before coating could prevent materials from rusting.
This discovery allows the coating to take place outside the small box, in the ambient air. The experiments demonstrated that perovskite cells made with the DMaFO additive can achieve an efficiency of nearly 25% on their own, comparable to the current record for perovskite cell efficiency of 26%.
The additive also improved cell stability.
Commercial silicon panels can typically maintain at least 80% of their performance after 25 years, losing about 1% of efficiency per year. Perovskite cells, however, are more reactive and degrade faster in air. The new study showed that the perovskite cell made with DMafO retained 90% of its efficiency after researchers exposed them to LED light that mimicked sunlight for 700 hours. In contrast, cells created in air without DMAfo rapidly degraded after just 300 hours.
While this is a very encouraging result, only 8,000 hours of testing can be done in one year, he said. Therefore, longer tests are needed to determine how these cells are maintained over time.
“It's too early to say that they're as stable as silicon panels, but we're on a good path toward that,” McGehee said.
The study brings perovskite solar cells one step closer to commercialization. At the same time, the McGehee team is actively developing tandem cells with a real efficiency greater than 30% and that have the same lifespan as silicon panels. The goal is to create tandems that are more efficient than conventional silicon panels and equally stable over a 25-year period.
With higher efficiency and potentially lower prices, these tandem cells could have wider applications than existing silicon panels, including possible installation on electric vehicle roofs. They could add 24 to 40 kilometers of range per day to a car exposed to the sun, enough to cover the daily commute of many people. Drones and sailboats could also work with these panels.
After a decade of research on perovskites, engineers have built perovskite cells that are as efficient as silicon cells, which were invented 70 years ago, McGehee said. “We are taking the perovskites to the finish line. If tandems work well, they certainly have the potential to dominate the market and become the next generation of solar cells,” he said.
