Perovskite solar cells are a mixture of organic molecules and inorganic elements within a single crystalline structure. Together they capture light and convert it into electricity. They can be manufactured more easily and cheaply than silicon-based solar cells. Perovskite solar cells can also be bonded to a flexible backing, which means they can be used for many applications where traditional solar panels are not feasible, such as on the roof and fenders of electric automobiles.
What they can’t do — yet — is match the efficiency or durability of conventional silicon solar cells. But researchers keep working to overcome those deficiencies in their quest to drive down the cost of solar panels and fit them to places where conventional panels would never work, such as the facade or windows of buildings.
An international team from China’s Shanghai Jiao Tong University, Switzerland’s Ecole Polytechnique Fédérale de Lausanne, and the Okinawa Institute of Science and Technology Graduate University in Japan claims to have developed perovskite solar cells with an efficiency of 18.1% by using a new configuration of cesium lead iodide (CsPbI3) perovskite cells. Researchers worked with crystals in their more stable beta phase. Previous research focused on the crystals in their alpha, or dark phase.
Although the alpha phase can ensure higher power conversion efficiency, according to PV Magazine it is unstable as the crystal structures rapidly degrade into a yellowish form increasingly unable to harvest light. The beta phase offers longer stability.
The researchers have found a way to repair the cracks that often emerge on the surface of perovskite cells by applying a choline iodide solution which heals them. The solution is said to help minimize the loss of electrons from CsPbI3 into adjacent layers and optimize the interface between layers in the cell. “This synergy between layers results in fewer electrons being lost and more electricity being generated,” says research paper co-author Luis K Ono.
Ultraviolet photoemission spectroscopy enabled the researchers to verify a smaller loss of electrons to adjacent layers after treatment with choline iodide, due to better alignment. “By repairing the cracks that naturally emerge this treatment led to an increase in conversion efficiency from 15% to 18%,” the researchers claim.
The scientists said their results show encouraging signs for the further development of CsPbI3 for solar applications but admitted the perovskite technology is still lagging. “For CsPbI3 to truly compete with silicon, the team will next work on the trinity of factors allowing silicon’s reign to continue: stability, cost and efficiency,” they say.
Manufacturers of conventional solar panels have nothing to fear from competition with perovskite cells just yet but with more research, the day could come when perovskites give those conventional solar panels a run for their money. Typical run of the mill solar panels today have an efficiency of around 19 to 20%. Perovskites are catching up quickly.