Solar Panels: Stacked Layers Could Pave the Way for Versatile, Collapsible Energy Harvesters | Science | New

Perovskites are compounds with a special crystal structure that have attracted considerable attention for their potential for optimizing solar energy harvesting technology. Solar cells made from perovskite have the potential to be more flexible and lighter than thin-film photovoltaics and more efficient than rigid silicon solar panels. In fact, researchers have already achieved efficiencies comparable to silicon solar cells – and are now working towards practical applications.

Solar cell efficiency can be improved by stacking two or more different cells on top of each other – if the different layers are particularly good at absorbing light from different parts of the electromagnetic spectrum, losses can be reduced compared to single layers .

This way, the overall efficiency of the solar panel – a measure of how much light falling on the cell is converted into electricity – is increased.

Due to their versatility, perovskites are exceptional components within these tandem solar cells.

In fact, perovskite and silicon tandem solar cells have achieved record efficiencies of over 29%, compared to just 25.7 and 26.7% for single cells made solely of perovskite or silicon, respectively.

Further advantages can be obtained by combining perovskites with materials such as copper-indium diselenide (CIS) or copper-indium-gallium diselenide.

These will enable the manufacture of lightweight and flexible tandem solar cells that can be installed not only on the roofs of buildings but also on vehicles and portable equipment.

It may even be possible to create solar panels that can be rolled up for storage and deployed when needed – as, for example, in blinds or awnings that can generate electricity at the same time as supplying power. The shadow.

In their study, photonics experts Dr. Marco Ruiz-Preciado and Professor Ulrich Paetzold of the Karlsruhe Institute of Technology and colleagues succeeded in producing tandem perovskite/CIS solar cells with a maximum theoretical efficiency of 24.9% (and 23.5% certified).

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Dr. Ruiz-Preciado said: “This is the highest efficiency reported for this technology and the first level of high efficiency achieved with a nearly gallium-free copper-indium diselenide solar cell in tandem.”

Lowering the amount of gallium in the cell results in a narrow “bandgap” of about 1 electron-volt which is very close to the ideal of 0.96 for a lower tandem solar cell.

The forbidden band is the name given to the part of the spectrum that a solar cell can absorb to produce electricity.

In a tandem solar cell, to achieve maximum efficiency, the band gaps must be set so that both layers produce similar currents. If the band gap of the lower cell changes, the band gap of the upper cell must be adjusted accordingly, and vice versa.

Normally, bandgap adjustments are made using high bromide perovskites, but this can lead to voltage work and phase instability.

However, because the researchers used CIS solar cells with a narrow bandgap at the base of the tandem cells, they were able to produce the top layers using low bromine perovskites, making the cells more stable and efficient.

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Professor Paetzold added: “Our study demonstrates the potential of perovskite/CIS tandem solar cells.

At the same time, he added, it “lays the foundation for future development to further improve their effectiveness.

“We have reached this milestone thanks to the exceptional cooperation within the framework of the EU PERCISTAND project and, in particular, thanks to our close cooperation with the Netherlands Organization for Applied Scientific Research.

Further preparatory work has been done, the team added, under the German-funded CAPITANO project.

The full study results have been published in the journal ACS Energy Letters.