Silicon has been to the solar power industry—not to mention the IT industry—what oil has been for the car industry: an essential element without which there would not have been an industry. Yet now there are challengers to the material that may turn out to be more efficient and one day replace it.
Perovskites are a group
of materials that have the same mineral structure as the original
perovskite, a mineral discovered in the 19th century. These materials are
not new to solar power research. They have some quite attractive properties
that make for enhanced panel efficiency at a lower cost than silicon. Now, an
international team of scientists have made a step further down the perovskite
solar road.
In a paper published
in Science, the team reported on the testing of a perovskite compound, CsPbI3,
that has demonstrated higher efficiency in solar power generation than
comparable materials.
The Institution of Mechanical Engineers quoted one
of the authors of the study as saying "We are pleased with results
suggesting that CsPbI3 can compete with industry-leading materials. From this
preliminary result we will now work on boosting the material's stability – and
commercial prospects."
Indeed,
stability happens to be a problem for perovskite materials when solar power
generation is a concern. As Imeche explains, CsPbI3 is often studied in its
alpha phase, a well-known configuration of the crystal structure appropriately
known as the dark phase because of its black colour. This phase is particularly
good at absorbing sunlight. Unfortunately, it is also unstable – and the
structure rapidly degrades into a yellowish form, less able to absorb
sunlight.”
It was this
second phase—the yellow phase—that the team focused on in this study.
Specifically, they focused on the cracks that appear in thin-film perovskite
solar cells during this phase in a bid to remove them as an obstacle to the
electricity flow. They used a chemical to do that, choline iodide solution, and
found that in addition to removing the cracks, the compound also improved
generation efficiency, from 15 to 18 percent.
The
discovery follows on the heels of another
one, made by researchers from KU Leuven university in Belgium. That
team found a way to make the perovskite stay in its black phase by sticking it
to a glass sheet and heating that to 330 degrees Celsius to make the perovskite
atoms stick to the surface. Once they are stuck to the glass, the perovskite
atoms can’t move and form the yellow phase of the mineral.
"There
are three pillars that determine the quality of solar cells: price, stability,
and performance. Perovskites score high on performance and price, but their
stability is still a major issue," said study author Dr. Julian
Steele, adding the researchers used the same type of perovskite as the authors
of the international study, which happens to be one of the highest-performing
but most unstable variations of the material. The results, therefore, should be
applicable to other unstable perovskites.
All this work is taking place in the lab at present, but perovskites
are certainly promising alternatives to the silicon solar cell. Solar
power is getting cheaper as materials become cheaper, but as silicon-based
solar technology is mature, it has little space to improve further. Emerging
technologies such as perovskite solar cells, on the other hand, have a lot of
space for improvement. Whether all these potential improvements will
materialize, however, remains to be seen.