International. The advantage of coatings produced by deposition of atomic layers is that they form a uniform and complete layer, even on rough surfaces.
Researchers at the University of Helsinki are developing necessary thin films into new types of halide perovskite solar cells and pairing ALD processes to provide increasingly affordable solar cells, enable their integration into objects, and consequently promote the transition to renewable energy.
The 2022 Millennium Technology Prize was awarded on 25 October to scientific professor Martin Green of UNSW Sydney, Australia, for his innovation that has transformed solar energy production.
In addition to silicon, other solar cell technologies are being investigated. The most promising new technique is based on the use of halide perovskites as a light-absorbing material.
The general chemical formula of halide perovskites is ABX₃, where A is an alkali metal or amine, B is tin or lead, and X is a halide.
The most commonly studied compound is lead and methylammonium iodide CH₃NH₃PbI₃. Perovskite solar cells are about to be commercialized, and some manufacturers believe they will be mainstream in a couple of decades.
"As these new types of solar cells can be transparent, they can be installed, for example, in windows. They are also flexible, which increases their uses," said university professor Marianna Kemell, who leads the research project funded by the Academy of Finland.
Although halide perovskite solar cells have achieved high levels of efficiency, problems with cell stability and lack of industrial-scale production techniques have been bottlenecks preventing their widespread adoption.
Produced through the deposition of the atomic layer
While pursuing a master's degree in chemistry, doctoral researcher Georgi Popov boldly chose halide perovskites and their atomic layer deposition (ALD) as the subject of his master's thesis.
"We identified the right chemicals and were able to design a reaction that allowed us to create a metal iodide coating through deposition for the first time. We were able to show that this can really be done through the deposition of the atomic layer," Popov said.
"The first successful test was carried out with lead iodide, which was then processed into perovskite CCH₃NH₃PbI₃ through an additional reaction. The research paper was published in the peer-reviewed scientific journal Chemistry of Materials. Subsequently, we also developed ALD processes for cesium iodide and perovskite CsPbI₃," Popov continued.
Coatings produced by atomic layer deposition are used in approximately 30% of silicon-based solar panels.
The ALD group led by Professor Mikko Ritala of the University of Helsinki has obtained promising results in terms of the adaptability of the technique to perovskite solar cells.
Uniform and complete layer on rough surfaces
The advantage of coatings produced by deposition of atomic layers is that they form a uniform and complete layer even on rough surfaces.
"If at some point we start making tandem solar cells, which combine a silicon cell and a perovskite cell, we'll know how to make that perovskite. We are developing the recipes and chemistry used to grow perovskite," Popov explained.
While the work currently being carried out is basic research, developing recipes and experimenting with small surfaces, the technique is applicable to large-scale production.
"Current plants that manufacture solar cells in China and elsewhere can adjust their equipment to produce ALD-coated solar cells," Popov added.
