AThe country has become accustomed to the blue-black shimmer on roofs. Occasionally, solar modules are now finding their way onto the walls of ambitious architectural projects. However, the façade as an energy supplier remains an exception. Because costs and effects don’t really go well together. But maybe also because blue and black veiled homes don’t pass every judgement.
Scientists at the Karlsruhe Institute of Technology (KIT) want to clear up at least this reservation. In cooperation with the Sunovation company, they have tested a process for coloring solar cells – not just in one color, but multicolored, for example to imitate white marble or Corten steel. In addition, the color is applied in such a way that the look of the cell modules does not vary just because you look at them from a different angle or when the sun is in a different position. That was often the problem with previous methods, according to the scientists at the Institute for Microstructure Technology, which belongs to the KIT.
They apply their color pigments using an inkjet process. For the cells, however, the choice is not silicon, but perovskite. The crystalline material is regarded as a beacon of hope in the industry. It is easy to process, shows promising efficiencies despite its comparatively short development time, and it is suitable for thin-film technology because perovskite can be evaporated extremely finely onto a carrier structure. So-called tandem cells, in which both silicon and perovskite are processed, show particularly good efficiencies of more than 29 percent under laboratory conditions. The substances convert other wavelengths of light better, so the energy yield increases when they combine their strengths.
If color comes into play, as in the KIT project, where the color pigments are printed in layers on the front of the solar module with the industrially tried-and-tested inkjet, this is of course only at the expense of efficiency. The project coordinator Helge Eggers takes a pragmatic view: “An integrated solar cell with low efficiency is better than a wall that does not supply any electricity at all.” An efficiency of almost 14 percent, as achieved with a white marbled prototype, is enormous, he says Eggers.
In the end, however, whether solar cells will prevail as a facade material will also be a question of price. It seems clear that perovskite cannot compete with concrete. It looks better in comparison with exclusive facades, made of polished stone or expensive marble.
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