Solar panels are more efficient than you’ve heard. This material could make them even better.

Renewable energy has been on the defensive recently. Following
the release of Planet of the Humans, the
controversial new climate change documentary
executive produced
by Michael Moore, fossil fuel–backed climate denial groups

are bashing wind and solar power
with renewed vigor,
regurgitating the film’s
flawed
,
ancient talking points
about the supposed poor performance and
unreliability of these energy sources.

Those talking points include the assertion that solar power is
wildly inefficient, something director Jeff Gibbs demonstrates by
visiting a solar farm in Michigan where photovoltaic panels convert
“just under 8 percent” of the energy in sunlight to
electricity. But that efficiency rating is, as the
photovoltaic-focused publication PV Magazine
puts it
, “from another solar era”: Today’s typical
silicon solar panels operate at around
22 percent efficiency
. And a new crystalline material called
perovskite could soon raise the solar efficiency bar much
further.


Solar photovoltaic cells
— the individual units that form a
solar panel, like the shingles on a roof — are wafer-like devices
made of materials called semiconductors that are capable of
converting sunlight to electrical energy. But even the best
semiconductors only capture a fraction of the light that strikes
them. Sunlight spans a wide range of wavelengths, and depending on
the properties of the semiconductor and the design of the cell,
some proportion of that light is reflected, some passes through,
and some is absorbed but converted into heat before the energy can
be put to use. Designing new solar cells that convert a larger
fraction of incoming sunlight into electrical energy, or that have
a higher
conversion efficiency
in solar power parlance, is one of the
most active areas of solar research today.

Perovskites first attracted the interest of the solar community
a little over a decade ago, when scientists discovered this
particular class of semiconductors has an outstanding ability to
convert sunlight to energy. Today, perovskites are at the center of
an effort to develop a new generation of thin-film solar cells that
are cheaper than, and around four times as efficient as, the solar
farm Gibbs visits in Planet of the Humans. The field is moving
fast: In late April, the U.S. Department of Energy’s National
Renewable Energy Laboratory
announced
it will be forming a U.S. Manufacturing of Advanced
Perovskites Consortium (US-MAP) to accelerate the development of
perovskite-based technologies.

According to US-MAP director Joseph Berry,
the consortium will allow government researchers, academics, and
private companies to pool resources and brainpower in order to
tackle the biggest hurdle facing the commercialization of
perovskite solar cells: Making these soft, easily degraded
materials more durable.

“That’s where the challenge for this technology is,” Berry
told Grist.

Perovskite refers to any compound that shares the same crystal
structure as the mineral perovskite, also known as calcium
titanate. The perovskites the solar industry is interested in
aren’t mined from the Earth, but cooked up in labs. Inside these
synthetic, or “hybrid,” perovskites, a mix of organic
compounds, metals, and halides (reactive elements that include
chloride, bromide, and iodide) sub in for calcium and titanium in
the crystal lattice. Because of their unique structure and chemical
composition, hybrid perovskites have a superpower: They’re
remarkably good at absorbing sunlight. “They are kind of awesome
in terms of their power conversion efficiency,” Berry said.

While silicon solar cells have a maximum potential efficiency of
around
29 percent
, a single perovskite layer can theoretically achieve
efficiencies of closer to 33 percent. And by synthesizing
perovskites that are sensitive to different parts of the solar
radiation spectrum and stacking them to create a tandem cell, the
efficiency can be boosted further — potentially above 40 percent,
said Jao Van De
Lagemaat
, who directs the chemistry and nanoscience center at
the National Renewable Energy Laboratory.

“That’ll take an enormous amount of engineering,”
Van
De Lagemaat
said. But some researchers have already
demonstrated that devices with two layers of perovskites are more
efficient than a single perovskite solar cell, he said. Traditional
silicon cells can be made more efficient by adding perovskites,
too.

Not only are perovskites inherently better at harvesting
sunlight than silicon, it’s potentially cheaper to mass-produce
solar cells that rely on them. While silicon cells are manufactured
via a complex process that involves
purifying silicon from quartz
in a high-temperature furnace,
perovskites can be fabricated at low temperatures using far less
energy, from cheap and readily available ingredients. Companies are
already working on a variety of low-cost techniques for applying
perovskites to a supporting surface, like a piece of glass, to turn
that surface into a thin-film solar cell. These include inkjet
printers, perovskite-based sprays, and roll-to-roll
manufacturing techniques
similar to those used for newspaper
printing.

But despite all their appeal, you can’t buy a perovskite solar
panel to put on your roof just yet. The reason? Easy-to-make
perovskites are also easy to unmake.

“The material itself intrinsically is not stable,” said

Letian Dou
, an assistant professor of chemical engineering at
Purdue University.

Perovskites dissolve in water, and they don’t hold up well
under heat — both of which are a problem if you’re trying to
manufacture a device to function atop a roof for decades. When a
solar panel is heated by the sun, Dou says, its temperature can
rise as high as 160 degrees F. At those temperatures, ions inside
perovskites move around very quickly, causing the molecular
structure to degrade. Even at room temperature, some “ion
migration” can occur, creating instabilities in the material.

However, emerging research suggests perovskites can be
stabilized by tweaking the chemical recipe. Recently, Dou and his
colleagues doped perovskites with a rigid molecule called a ligand,
allowing the material to remain stable at temperatures of up to 212
degrees F. The research,
published last month in Nature, is preliminary — the tests were
done at the lab scale, and on timescales of days, not decades —
but it points to a “promising direction” for making
commercially ready perovskites, Dou says. In a March study
published in Science, scientists at the National Renewable Energy
Laboratory made perovskites using three halide elements instead of
the usual two, and
found
that the material degraded less than 4 percent after
1,000 hours of continuous operation in sunny conditions.

Berry says that when the Department of Energy (DOE) first
started investigating perovskites in solar applications back in
2013, “lifetimes were measured on the order of hours, maybe tens
of hours. And we’ve made a three orders of magnitude change in
that. But the challenge is to make another couple of orders of
magnitude change.”

The new US-MAP consortium aims to accelerate these efforts by
enabling private companies, government researchers and academics to
share new ideas and research facilities, and by encouraging them to
join forces to conduct more ambitious tests. While all of the
founding organizers are bringing their own research funds to the
table, the consortium plans to seek additional funding from federal
agencies like the DOE, as well as various state and local
government programs and industry partners.

“The idea is we want to sort of band together,” Van De
Lagemaat said. “There is quite a bit of research that can be done
collectively that doesn’t really impact each individual
company’s special sauce, but that really helps bring the entire
area forward.”

Some of US-MAP’s commercial partners are already thinking
about how to get the first perovskite solar panels out into the
wild. Swift Solar, a
California startup founded in 2017, is planning to stack two
different layers of perovskites in tandem to create lightweight,
high-efficiency solar cells that initially will be marketed for
mobile applications like drones, satellites, and the lighting and
air conditioning systems on trucks. Swift Solar co-founder Kevin
Bush says vehicles are a good place for the first generation of
perovskite solar panels to shine, both because portability is at a
premium and because mobile markets “might only need five to 10
years’ stability, and it’s just a lot easier to promise that”
right now.

“I think it’s nice to have markets that are initially not
that demanding” in terms of longevity, Bush said, “so we can
prove the technology out more.”

Van De Lagemaat doesn’t think perovskites will ever replace
silicon wholesale in the solar power world. But he does think they
will come to play “a very large role in the power market,”
partly because rising solar efficiency and manufacturing
improvements have caused the price of solar power to fall
dramatically in recent years. While this price drop is good for
consumers, it also means there’s less money to invest back into
new silicon solar factories, which are expensive to build.
Technologies that require less up-front capital investment, like
perovskites, might ultimately be necessary to build the amount of
solar power the world needs in the coming decades, he says.

If that hunch is correct, Planet of the Humans’ already
outdated criticism of solar efficiency will soon feel
prehistoric.

This story was originally published by Grist with the headline
Solar panels are more efficient than you’ve heard. This material
could make them even better.
on May 13, 2020.

Source: FS – All – Ecology – News 2
Solar panels are more efficient than you’ve heard. This
material could make them even better.