An international team of researchers has developed a new method to improve the durability (Improved durability of low-cost solar cells made from nanocrystals) of inverted perovskite solar cells – an important step for the commercialization of emerging photovoltaic technology that can reduce the cost of solar energy.
Unlike traditional solar cells, which are made from ultra-pure silicon wafers, perovskite solar cells are made of nano-sized crystals. Perovskite crystals can be dispersed in liquid and then coated on the surface using a cheap and efficient method.
It is possible to modify the wavelength of light absorbed by perovskites by changing the ratio and chemical composition of the crystal film. Perovskite layers tuned to different wavelengths can even be stacked on top of each other, or on top of traditional silicon cells, leading to “tandem” cells that absorb more of the sun’s spectrum different devices now.
The latest work, published in the journal Science, involves researchers from the University of Toronto, Northwestern University, the University of Toledo and the University of Washington.
“Perovskite solar cells can overcome the natural performance weakness of silicon solar cells,” says study co-author Ted Sargent, who recently joined the chemistry department and engineering department. Electric and Computer Science from Northwestern University, and remains in partnership. U of T Engineering, where he has a laboratory.
“They also lend themselves to a manufacturing process that consumes less material than silicon. But one area where perovskites still fall behind silicon is their longevity. In this study, we used a logical design method to solve this problem in a new and unique way.
In recent years, Sargent and his colleagues have made many advances that improve the performance of perovskite solar cells. But while much of the previous work focused on improving efficiency, their new work looks at sustainability challenges.
Chongwen Li, a postdoctoral researcher who moved to U of T Engineering explains, “One of the main weaknesses for these types of solar cells is the bonding between the perovskite layer and the adjacent layer, which we calls for air transportation.” from the University of Toledo and is one of the paper’s co-authors.
“These adjacent layers remove electrons or holes from the circuit. If the chemistry between these layers and the perovskite layer is damaged by light or heat, electrons or holes cannot enter the circuit, reducing the overall efficiency of the cell,” Li explains.
To solve this problem, the international research team returned to the original principle. They used computer simulations based on density functional theory (DFT) to predict which molecules would best bind between the perovskite layer and transport charges.
“Previous research has shown that molecules known as Lewis bases are good at creating strong bonds between these layers,” says Bin Chen, a postdoctoral researcher in Sargent’s lab, who is now assistant research professor at Northwestern University and co-author of the paper. the book.
“This is because one end of the molecule binds to lead atoms in the perovskite layer and the other binds to nickel in the transport layer. Our simulations predict that Lewis bases with phosphorus compounds will have the best effect.
In the laboratory, the team tested different systems of phosphorus-containing particles. Their tests showed the best performance with a substance known as 1,3 bis(diphenylphosphino)propane, or DPPP. The group built inverted perovskite solar cells with DPPP, and others without.
They put the two models through tests that demonstrate the conditions the solar cells will have in the field, giving them light of similar power to the sun. They also tried to expose them to high temperatures, both in light and in the dark.
“With DPPP, under normal conditions – that is, without additional light – the conversion efficiency of the cell remains high for about 3,500 hours,” Li says.
“Perovskite solar cells that were previously published in the literature usually show a significant loss of efficiency after 1,500 to 2,000 hours, that’s a big improvement.”
Li says the group has filed a patent for the DPPP process and has attracted interest from commercial cell manufacturers.
“I think what we have done is to show a new way forward – that DFT simulations and rational design can show a promising solution,” he says.
“But there may be better molecules out there. Ultimately, we want to get to the point where perovskite solar cells can compete with silicon, which is the current photovoltaic technology. This is an important step in this direction, but there is still much to do.
Source: University of Toronto
