Researchers at Eindhoven University of Technology (TU/e) and research institute ECN (part of the Solliance collective) have found that adding a thin layer of aluminum oxide helps protect a perovskite solar cell against humidity, as well as add a yield boost of 3%.
The scientists covered the sensitive layer of perovskite with a few atomic layers of aluminum oxide to protect against degradation caused by humidity. These layers are contained within the solar cell, between the layers of perovskite and electric contact. The researchers chose aluminum oxide (Al2O3) since it can form immediately on any kind of surface. The team explained that despite the fact that Al2O3 has electrically insulating properties, it can still be used as a buffer layer between the semi-conductive perovskite and the conductive contacts by limiting the thickness of the layer to one nanometer or less. This way, charge carriers can then tunnel electrically through the insulator layer.After these thin layers were applied with precise composition by atomic layer deposition (ALD), the researchers compared the stability of these cells with identical cells without the layers. The complete cells were not given any further protection against humidity with sealed packaging. Two months after being exposed to a humid atmosphere the cells containing the Al2O3 layer reached 60-70% of their original yield while the reference cells managed only 12%.
In addition, the added layer boosted the yield from 15% to 18%. "That was an extra bonus for us," the team said. "We had not expected this and we cannot exactly explain why it is. But we will certainly be investigating." Whether the layers will raise the perovskite cell record is apparently difficult to say, as "they are constructed in a completely different way to the simple, scalable structure we chose. But the stability will very probably also increase in those cells."
The researchers claim that fact that the protective aluminum oxide layer is not incorporated on the outside, as often attempted by other researchers, also makes it possible to apply a broad range of materials on both sides of the solar cell and allows the maximum penetration of light in the perovskite layer and thereby the optimum utilization of electrical current.