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Silicon solar cells are a well-established technology for generating electricity from the sun. But it takes a lot of energy to produce it, and it’s hard and can be brittle.
However, a new class of solar cells matches their performance. What’s more, they can now be printed with special inks and flexibly wrapped around uneven surfaces.
We have developed the world’s first fully rollable, printable solar cell made of perovskite, a material that is much less expensive to produce than silicon. If we can also improve their efficiency, this indicates that solar cells can be made cheaper on a much larger scale than ever before.
The silicon solar cells that are recognizable to us are very limited. If enough are made to cover our needs, we could run out of materials to make them by 2050. For that, we need something new and lots of it. A perovskite solar cell appears to fill that gap.
Perovskites are a crystalline structure made of inorganic and organic components, named after Lev Perovsky, a Russian mineralogist of the 17th and 18th centuries.
Perovskite solar cells first appeared in research laboratories in 2012 and caught the attention of researchers because of two factors: their ability to convert sunlight into electricity, and their ability to be made from a mixture of inks.
In research laboratories, using highly controlled production methods in environments in which oxygen and water are completely removed, perovskite solar cells can now match the electricity generation of silicon solar cells. This is an amazing achievement.
But cheap perovskite solar cells that scrap silicon have not yet been manufactured on a commercial scale. So what if these materials were produced using the same kinds of processes we use to print regular packaging?
Recently my colleagues and I demonstrated that a roll of plastic film can be loaded into a press, and working perovskite solar cells appear at the other end. However, it is not as simple as pouring ink into a desktop printer.
For one thing, scientists have found that to achieve record efficiencies, the semiconductor and perovskite layers in this new form of solar cell need to be extremely thin—between 50 and 500 nanometers (about 500 times smaller than a human hair).
Also, the inks used to print them require highly toxic solvents. But, after many years of effort, we have now formulated inks without toxic solvents that are compatible with the aperture coating process – a well-established industrial technology originally used to produce photographic film.
How does our solar cell work?
The printed perovskite layer generates free electrons from the energy provided by the light that strikes it. The perovskite semiconductor then prevents these electrons from being reabsorbed with a good energy conversion efficiency (ratio of light energy to electrical energy out).
One problem remained: how to extract the electric charge. In the past, this has been achieved by heating gold in a vacuum until it vaporizes, and capturing the vapor on a perovskite solar cell to form electrodes.
We took a different approach, creating a carbon ink compatible with both the perovskite material and the hole die coating process. The result is loads of flexible, rollable solar cells that come off the press ready to generate power.
More work required
Perovskite solar cells have shown high performance in research laboratories and are now proving their potential to make the leap to high-volume manufacturing. But the job is not over yet.
The 10% energy conversion efficiency achieved by these rotatable printed cells is advantageous, and is higher than that of the first commercial silicon plates. But it lags behind the typical conversion efficiency of 17% for domestic solar panels in use today.
We know that other augments are available by utilizing high-performance perovskite chemistry.
There is an engineering challenge that must be overcome in order for large-scale, commercially produced perovskite solar panels to match silicon power generation. Further improvements in the life stability of perovskite solar cells are also needed—through a combination of chemistry, device design, and other strategies such as protective coatings and laminated barrier films.
In short, research needs to focus on turning what happens in labs into real devices. But the possibility of producing hundreds of thousands of square meters of flexible perovskite solar cells is now a step closer.