Perovskite + Silicon Solar Panels Hit Efficiencies Of Over 30%

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In most industrialized countries, solar panels contribute between a quarter and a third of the total cost of building a solar farm. All other costs (additional equipment, financing, installation, permits, etc.) make up the bulk of the cost. To get the most out of all these other costs, it makes sense to pay a little more to install efficient panels that convert more of the incoming light into electricity.

Unfortunately, advanced silicon panels already have an efficiency of about 25 percent, and there is no way to increase the material efficiency above 29 percent. And there's a huge price jump between that and the kind of specialized, high-efficiency photovoltaic equipment we use in space.

These expensive panels are made of three layers of photovoltaic material, each tuned to a different wavelength of light. So, to achieve something in the middle on the cost/performance scale, it makes sense to develop a two-layer device. Some progress has been made in this regard this week, with two separate reports of double-layer perovskite and silicon solar cells with efficiencies in excess of 30 percent. Right now, it doesn't last long enough to be useful, but it could point the way to better materials.

wear low

The concept of a two-level photovoltaic device, called a tandem, is very simple. The top layer must absorb high-energy photons and convert them into electricity, while remaining transparent to other wavelengths. Therefore, the lower energy photons must be absorbed by the substrate. Silicone, which absorbs most of the red part of the spectrum, is an excellent candidate for undercoating. This leaves the question of what it might mean to be on top.

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Perovskites are an interesting candidate. This is an entire category defined by the structure of the crystals that can form; It can be made from a variety of unrelated chemicals. This has several important advantages, as it means that you can choose some very cheap starting materials that can be combined with a perovskite crystal. Many perovskites are also readily produced from source material solutions, allowing us to incorporate photovoltaic perovskites into a wide variety of devices.

The big problem was that many of these crystals are not particularly stable and break down into raw materials over time. And that time can be weeks or months for some promising material. Some progress has been made to extend their lives, but we are not yet at the point where it makes sense to make perovskite sheets.

Another nice feature of perovskites is that by carefully choosing the raw materials, you can tune the maximum wavelengths absorbed by the resulting crystal. So you can choose a wavelength that matches silicon well. And there was some evidence of success from tandem perovskite cells, but their efficiency was not much higher than what silicon could achieve on its own.

Very nice, people have done it twice.

In a recent issue of Science, two papers report much higher efficiency than perovskite / silicon tandems. Newspapers use different methods to get there, but accidentally end up in the same place.

One of them, from a large collection in Europe, focuses on the physical structure of the plate. The surface of some high-energy silicon panels is covered with countless microscopic pyramids. They increase the total light absorbed, since any photon reflected by one of the pyramids is more likely to end up in the second, increasing the chance that it will eventually be absorbed. But coating them with a layer of perovskite usually fills the space between the pyramids and then creates a flat surface on top.

The aim of the work was to find a way to align the perovskites with the silicon surface and thus create pyramids on top of the silicon. To do this, the researchers tested different additives in a solution containing perovskite. They finally settled on something called 2,3,4,5,6-Pentafluorobenzylphosphonic acid, which is a benzene ring with one carbon attached to a phosphate and the rest to a fluorine. This slows down the crystallization process, causing the perovskites to cover the silicon evenly, replicating the Sea of ​​Pyramids.

However, during this process, chemical additives were extracted from the perovskite crystals and coated on their surface. Once there, it helped mitigate electron capture defects, allowing the perovskites to reach the current collector rather than falling back into orbit. As a result, the efficiency exceeded 31 percent.

Other work, also the result of a European collaboration, focused on optimizing the silicon-perovskite mixture. Calculations that tell us the wavelength of maximum absorption of perovskites can be performed to maximize the amount of light converted into electricity. From there we can determine the chemical formula you need to get it.

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Using this information, the researchers improved the interface between the perovskites and the existing collector, deliberately trying to reduce the loss of useful electrons, which other groups have accidentally achieved. To do this, they added an organic molecule that can accept or donate electrons, thereby acting as a holding area while the electrons find their way into the existing complex.

The end result was perovskites, which on their own were more than 20 percent efficient. When combined with silicon in a tandem device, the efficiency exceeds 32 percent.

The work will be completed

The good news is that there is plenty of free space left, with calculations based on these devices showing they can achieve efficiencies of around 45 percent. Regardless, they are already more efficient than silicon alone, and perovskites retain their advantages in the form of low cost and ease of operation.

The big problem is that the hardware life is very short. Even the most stable device developed by the first group had its initial efficiency reduced to 80 percent after only 66 hours of exposure to sunlight. The second was slightly better, driving for 347 hours before dropping below 80 percent. However, if you assume 12 hours of sunlight a day, that's less than a month's use, which is terrible.

We know how to make perovskites last longer. But it is not clear whether they maintain decent efficiency in tandem settings. So there's a lot of work to be done before we try to commercialize these things, and there's a chance that another tandem technology will be in the works soon. But the work is likely to continue because high-efficiency panels can go a long way toward expanding renewable energy at the rates we need.

Nauka , 2023. DOI: 10.1126/science.adf5872, 10.1126/science.adg0091 (via DOI).

Erkan Eden: Perovskite tandem solar cells/high-GWP perovskite solution solved.