In a bid to improve the efficiency and lower the cost of solar cell technology, scientists at Iowa State University have developed perovskite-based cells that can withstand much greater temperatures while also maintaining efficiency. The study is based on a tandem structure that stacks two kinds of cells, perovskite and silicon, on top of each other, each using different, complementary parts of the solar spectrum to produce power, and was shown to improve efficiency by as much as 50%.
Although perovskites have a crystal structure and offer useful electro-optical properties for cheap, lightweight, efficient and flexible solar cells, hybrid organic–inorganic perovksite solar cells decompose when exposed to high temperatures, which is problematic if they are located in a hot, dry desert, for instance. However, in this new research, reported in ACS Applied Energy Materials [Gaonkar et al. Appl. Energy Mater. (2020) DOI: 10.1021/acsaem.0c00010], hybrid organic–inorganic perovskite materials were investigated as a useful tandem partner for silicon cells.
By removing organic components in the perovskite material, especially cations, which were substituted with inorganic materials such as cesium, the material became more stable over higher temperatures. The solar cells were stable and exhibited no thermal degradation even at 2000C over three days, and the efficiency was reasonable for that bandgap. As corresponding author Vikram Dalal told Materials Today, “We found that the elimination of organic cations made the material itself stable at least up to 3000C, and the cell up to 2000C in our preliminary experiments. We are now trying to push these limits to higher temperatures.”
The team also produced a vapor deposition fabrication technique that builds the perovskite material a thin layer at a time in a consistent way and leaving no contaminants. Such an approach is already being used in industry, and so can be scaled up commercially. They also tried replacing the iodine in perovskite materials with bromine, which made the cells much less sensitive to moisture, but altered the cells’ properties, lessening efficiency and how well they worked in tandem with silicon cells.
Using an all-inorganic material and removing the unstable organics, as well as demonstrating the use of vapor deposition techniques that are inherently scalable and reproducible for producing commercial scale solar cell modules, are key breakthroughs. The team now hopes to optimize the cell to make it more efficient at converting solar energy into electricity using new combinations of materials, and to improve stability against moisture and against photo-induced degradation of the solar cell device.
“We found that the elimination of organic cations made the material itself stable at least up to 300C, and the cell up to 200C in our preliminary experiments. We are now trying to push these limits to higher temperatures.”Vikram Dalal
"X-Ray diffraction data on inorganic, thermally stable perovskite film before and after anneal at 300C for 24 hours. There is no change in the spectrum, no PbI2 peak after anneal (unlike the case for a hybrid organic–inorganic perovskite, which would show a distinct PbI2 peak after anneal at ~100C), showing that there is no decomposition of the inorganic perovskite material."