Perovskite-based solar cells: young technology, high return
Certain organometallic compounds can form perovskite crystals with semiconductor properties. This type of material was only applied in solar cells for the first time in 2009. Since then, these so-called perovskite solar cells have been shown to have ever-higher energy yields in scientific laboratories. In only a few years’ time, an efficiency was demonstrated equal to that of the best Si solar cells. We therefore have extremely high expectations of this thin-film PV technology. Everything also indicates that these perovskite solar cells could form a good tandem with traditional c-Si solar panels. It is expected that this tandem combination could produce solar panels with yields of over 30%.
Benefits of perovskite
Perovskite has a crystal structure that takes its name from a Russian researcher. Using 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.
In principle, with the current state of perovskite solar cell technology, the same module efficiency can be achieved on glass or foil as currently with m-cSi, CdTe or CIGS: namely, between 15 and 18%. Currently, we have been able to demonstrate a module efficiency of 10% with available production processes within Solliance. We hope to demonstrate a module efficiency of 15% in 2017. This, together with the fact that the manufacturing process can be very cheap, could result in a paradigm shift 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 so-called ‘tandem technology’. In combination with Si solar cells, efficiency could in principle end up exceeding 30%. (By comparison, the best c-Si solar cells can obtain an energy yield of 25.2% in the laboratory).
Solliance has the technology and equipment in-house to develop and demonstrate the processes required to upscale perovskite PV modules, both sheet-to-sheet and roll-to-roll. To do so will still require a lot of research. A few important aspects in this regard are:
We obviously aim for PV modules with the highest possible energy yield. To this end, it is necessary to understand which factors affect efficiency, and how they can be influenced.
Obviously, the solar cells and modules must also be stable when used. This means that the yield may not fall more than 20% if used for twenty years. Factors that can adversely affect stability are water, air, temperature, electrical influences of the PV system, sometimes even light, and almost always a complex combination of all of these factors.
Therefore, we are constantly looking for the causes of potential instability and trying to eliminate them by using different materials and other 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.
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.
Solliance is identifying the various potential risks and investigating alternatives. We are currently also looking into tin and the less harmful bismuth as a lead replacement.
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.
Dyesol, Panasonic, Solartek and Nano-C are all companies participating in the Solliance Shared Research Programme on perovskite-based solar cells.
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