Perovskite-based solar cells: young technology, high efficiency potential

A few years ago, Perovskite solar cells already demonstrated an efficiency comparable to that of the best Si solar cells. Expectations for this thin film PV technology are therefore high. There are many indications that these Perovskite solar cells can form a good tandem with the traditional c-Si solar panels. It is expected that this tandem combination will be able to produce solar panels with efficiencies of more than 30 percent.

Benefits of Perovskite

Perovskite is a crystal structure that takes its name from a Russian researcher. The use of Perovskite as a semiconductor in PV modules has important advantages:

• The raw materials required to produce this semiconductor perovskite are very cheap.
• What’s more, you only need a very thin layer of perovskite in a solar cell, resulting in even lower material costs.
• Perovskite can be applied with a relatively simple deposition process (the application of the layers on a given substrate), so that no expensive machines are required.
• The perovskite layers can be deposited at low temperatures, which also keeps production costs low.

With the current status of Perovskite solar cell technology, the same module efficiency can be achieved on glass or foil as is currently being realized with (m)cSi or CdTe or CIGS: between 15% and 18%. At the moment we have already been able to demonstrate a module efficiency of 10% with available production processes at Solliance. We aim to demonstrate a module efficiency of 15% in 2018. This achievement, and the fact that the manufacturing process can be very cheap, could lead to a paradigm in the solar cell world.

Just like CIGS, Perovskite can be used on glass, but also on flexible foils, which can in turn be integrated into numerous products, such as automobile roofs or siding. If a transparent substrate is used such as glass or plastic, the perovskite-based solar cells could also be made semi-transparent, which could, for example, be used in window applications

Transparency is also needed for the promising application of Perovskite solar cells in the so-called tandem technology. In combination with Si solar cells, the efficiency could exceed thirty percent. (By way of comparison, the very best c-Si solar cell achieves an energy yield of 25.2% in the laboratory).

Our Perovskite research

Solliance has the technology and equipment to develop and demonstrate the scale-up processes of Perovskite PV modules, both sheet-to-sheet and roll-to-roll. Therefore, much research still needs to be done. Important aspects to be addressed include:

• Improved efficiency: we are obviously striving for PV modules with the highest possible energy yield. Therefore we need to understand which factors have an effect on the efficiency and how they can be influenced.
• More stability: it is important that the solar cells and modules are stable when used. This means that the efficiency must not fall by more than 20% after twenty years of operation. The factors that can affect stability are water, air, temperature, electrical influence of the PV system, sometimes even light and almost always a complex combination of these factors.That is why we are constantly looking for any causes of possible instability and trying to eliminate those causes by using different materials and different processes. A disadvantage of Perovskite, for example, is that it is not resistant to water. This places high demands on the barrier layer, the protective layer of PV modules. We have achieved good results using Atomic Layer Deposition (ALD). By applying this technology to the inner layers, a less strong barrier layer is needed to make the modules moisture-resistant. Solliance has patented this innovation.
• Reduction of toxicity: A disadvantage of perovskite PV modules is that they will contain a small amount of lead: approximately half a gram per square metre. Because lead could end up in the environment if a solar panel were to become damaged, we are investigating the extent of the resulting harm and how it could be reduced.
  As long as toxicity is still considered a risk, Perovskite can be ‘wrapped’ in glass panels. These could then be used in solar parks, where energy is generated on a large-scale in a controlled and safe manner using solar panels.