An international team of researchers has developed a new technique to enhance the durability of inverted perovskite solar cells, which can be an essential step toward commercializing emerging photovoltaic technology and significantly reducing the cost.

The work was published in Science and included researchers from the University of Toronto, Northwestern University, the University of Toledo, and the University of Washington.

Perovskite solar cells are made from nano-sized crystals, unlike traditional solar cells built out from high-purity silicon wafers. These perovskite crystals can be dispersed into a liquid and spin-coated onto a surface using low-cost and well-established techniques.

“Perovskite solar cells have the potential to overcome the inherent efficiency limitations of silicon solar cells,” said study co-author Ted Sargent.

However, one place where perovskites still lag silicon is in their long-term durability.

Perovskite Prone to Degradation

One key point of vulnerability in these types of solar cells is the interface between the perovskite layer and the adjacent layers, called the carrier transport layer.

These adjacent layers extract the electrons or holes flowing through the circuit. In cases where the chemical bonding between these layers and the perovskite layer gets damaged by light or heat, the electrons or holes can’t get into the circuit, lowering the cell’s overall efficiency.

To address this issue, the international research team used computer simulations based on density functional theory (DFT) to predict what kind of molecules would best create a bridge between the perovskite layer and the charge transport layers.

Lewis Acids Prevents Degradation

“Previous research has shown that molecules known as Lewis bases are good for creating strong bonding between these layers,” said Bin Chen, a research assistant professor at Northwestern University and a co-author of the paper.

The simulations also predicted that Lewis acids, which contained phosphorus, would have the best effect.

In the lab, the team tried out various formulations of phosphorus-containing molecules. Their experiments showed the best performance with a material known as 1,3 bis (diphenylphosphino)propane, or DPPP.

The team built inverted perovskite solar cells that contained DPPP and some without it.

“With DPPP, under ambient conditions—that is, no additional heating—the overall power conversion efficiency of the cell stayed high for approximately 3,500 hours,” the researcher said.

The perovskite solar cells that have been previously recorded, tend to have seen a significant drop in their efficiency after 1,500 to 2,000 hours – thus, this is a considerable improvement.

The team has applied for a patent for the DPPP technique and has received interest from commercial solar cell manufacturers.

“I think what we’ve done is to show a new path forward—that DFT simulations and rational design can point the way toward promising solutions,” he says.

Researchers at the École Polytechnique fédérale de Lausanne and Sungkyunkwan University in South Korea have recently identified the cause behind the degradation of perovskite solar cells and developed a technique to improve its stability.

In the same month, researchers at the Helmholtz-Zentrum Berlin said that they had produced perovskite solar cells to achieve efficiencies of well above 24%, which are resistant to drop under rapid temperature fluctuations between -60 and +80 degrees Celsius over one hundred cycles.