Vacuum boost for tandem perovskite solar cells
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A study in Germany has shown that vacuum processes can speed up the production of lightweight, low cost perovskite solar cells.
The study by the Karlsruhe Institute of Technology (KIT) and NREL in the US analysed both solvent and vacuum-based production processes for perovskite solar cells.
The study identified a variety of solutions and conclude that vacuum-based technology is competitive in terms of real parameters such as energy costs, production yield, material costs, decommissioning costs, and recycling costs, particularly for tandem cells with a perovskite layer on top of textures silicon.
“Not only is vapour deposition the number one choice of industry when bringing a new thin film product to market, our analysis shows that it can also be cost competitive with solution deposition,” said researcher David Moore of NREL.
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Over the past decade, perovskite-silicon tandem solar cells have demonstrated accelerated development and in research, efficiencies of more than 33 percent have been shown, exceeding by far those of conventional silicon-based solar cells.
One of the major challenges is the unresolved question of which process is best suited for mass production of perovskite solar cells.
“98 percent of all scientific studies in 2022 dealt with solvent-based processes. Vacuum-based processes, on the other hand, have proven themselves in industry for many decades. Although they can decisively advance the commercialization of solar cells, they are heavily underrepresented,” said Professor Ulrich W. Paetzold from the Institute of Microstructure Technology and Light Technology Institute of KIT.
Solvent-based manufacturing uses inks in which organic and inorganic salts are dissolved in a solvent. These inks can be deposited on the substrate surface using various printing techniques. Vacuum-based manufacturing uses dry and solvent-free processes with materials that are sublimated in a vacuum under heat supply. It is also possible to combine both processes for the production of perovskite solar cells.
In their study, the authors analyzed the advantages and disadvantages of both methods. The dominance of solvent-based production in research is mainly due to its ease of use in the laboratory, its good efficiency under laboratory conditions, and its low cost. This can also be used for scalable roll-to-roll production.
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Vacuum-based production is associated with slightly higher investment costs. Deposition rates are still lower than those of solvent-based research production. The good reproducibility of deposition, the ease of process control, the availability of industrial process equipment, and the easy scalability of deposition from small lab-scale solar cells to application-relevant product areas make vacuum-based production highly attractive for commercialization.
“Vacuum-based manufacturing performs better than its reputation,” says researcher Tobias Abzieher at KIT. Industry is already very interested in vacuum-based processes for the production of perovskite solar cells, even though they differ from the method mainly used in research.
Of particular interest for an industrial application of vapour-processed perovskite solar cells are fully evaporated layer stack sequences, in which all functional layers of the solar cell are prepared by vapour-based approaches.
This was pioneered in 2014 with fully evaporated perovskite solar cells with efficiencies as high as 10.9%. This lowers the complexity of the fabrication process compared to mixed approaches also employing solution-based approaches and most importantly enable a simple upscaling of the deposition process toward industrially relevant device areas.
Promising prototype solar modules have been demonstrated with low upscaling losses comparable to thin-film technologies and can be used more easily with tandem applications in combination with textured silicon bottom solar cells.
The high conformity of vapour-deposited layers means high-quality film formation can be achieved even on highly textured silicon bottom solar cells which is usually tricky to access by solution-based approaches.
To take full advantage of the scaling effects of vacuum-based processes, further improvements are needed, the researchers say. It is important to study the quality of deposition to improve efficiency. In addition, the deposition rate needs to be increased significantly.
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