Tandem solar cells achieve 34% efficiency
What kind of tandems do you have here?
Since the 1950s, solar panels have been made from silicon—the de facto industry standard. But “pure silicon” cells have long since reached their theoretical efficiency limit. Perovskite, a material with the same crystal structure as the mineral calcium titanium oxide, the first perovskite crystal to be discovered, helps circumvent this limitation. Perovskite compounds typically have the chemical formula ABX3, where A and B are cations and X is an anion that binds to both. A wide variety of elements can be combined to form perovskite structures.
The idea of combining silicon with a perovskite coating is not new. Back in 2012, researchers figured out how to create a stable thin-film perovskite solar cell with an efficiency of converting photons into electrons of more than 10%. At that time, scientists used lead halide perovskites as a light-absorbing layer.
The tandem element absorbs a wide part of the spectrum. The thing is that perovskite can absorb energy from the blue and ultraviolet range, and silicon works better in the red and infrared parts. Perovskite is applied in the form of a special solution, which then crystallizes. Crystals appear on the surface of the solar cell. There is one problem here – they are not very stable. The crystalline structure is destroyed over time. This is not the fastest process, but still the applied layer gradually degrades, and stable and strong heating increases the rate of degradation.
What if we add tetrahydrotriazinium?
A team of scientists from Turkey and Saudi Arabia decided add one more to this warm company of elements and compounds – tetrahydrotriazinium. Its peculiarity is in neutralizing free positive hydrogen ions, that is, in fact, protons. And they are the reason for the destruction of the crystal lattice of perovskites.
Researchers developed a special process for stabilizing a solution with all the necessary components. They managed to find the optimal conditions for the formation of perovskite crystals with protection from tetrahydrotriazinium. They coated a regular solar cell with the resulting stable solution, achieving an efficiency of 34% in the laboratory. To verify the results, the researchers sent a sample to an independent European lab. There, they obtained almost the same result – 33.7%.
The technology is not perfect. There is another problem: if the new type of tandem solar cell is exposed only to light, everything is fine. But when it is exposed to both light and heat, the conversion efficiency begins to gradually drop. And this process is fast – 10% in about three months. So the technology is not yet ready for commercial use.
Scientists continue their work and hope that they will be able to increase the stability of perovskite solar cells.
What about commercial samples?
Perovskite solar panels are already on sale. The most energy-efficient of them are produced by the German company Oxford PV. The Oxford PV perovskite-silicon solar cell has achieved an efficiency of 26.9%. This is 1.9% higher than the best modern silicon panels of the same area. And, as I said above, this is not the limit for tandem designs.
The area of the German module is about 1.6 m², and its weight is less than 25 kilograms. It is universal: such a solar panel can be placed on the roof of an enterprise or a residential building. According to the company representatives, the efficiency of the “solar farm” made of new type elements is about 20% higher than the usual one made of silicon panels. Of course, with the same area.
“Over the past decade, our team has been tirelessly demonstrating the potential of perovskite in silicon tandem solar cells, setting and breaking efficiency records. Now, we are taking the next steps to commercialize this highly efficient solar technology to support our vision of an all-electric future,” said Chris Case, chief technology officer at Oxford PV. The company manufactures its cells in Brandenburg an der Havel, Germany, and is now planning to scale up production.
Solar panels are becoming an increasingly popular source of energy, of course, in regions with sufficient levels of insolation. They are gradually becoming cheaper, and their efficiency, as we can see, is growing. So the technology clearly has a future.
