China's Solar Dominance Faces Challenge From Ultrathin Cell

"TOKYO -- China's near-monopoly on the solar-energy market has prompted the U.S. and allies to step up the search for workarounds. Engineers believe they have found one in a type of solar cell that looks and feels like camera film.

Japan is pushing the technology with subsidies and other support, a sign of how renewable energy, alongside other high-tech fields such as semiconductors, has become a geopolitical football.

Chinese firms control over 80% of the global supply chain for silicon solar panels, and China's share of polysilicon, the core material for the panels, is even higher. "The world will almost completely rely on China for the supply of key building blocks for solar panel production through 2025," the International Energy Agency says.

In the U.S., the Biden administration is seeking to build a domestic supply chain for solar panels. 

Japan, also looking for a homegrown solar solution, is focusing on what are called perovskite solar cells that don't use any silicon.

Invented by Japanese scientist Tsutomu Miyasaka, the cells use minerals forming a crystal structure called perovskite, which can be used in a device to turn the sun's rays into electricity.

A key element in manufacturing perovskite is iodine. While hardly a resources powerhouse, Japan happens to be the world's second-largest producer of iodine after Chile, accounting for around a third of global production.

"Look at what China is doing with semiconductors. That's bullying," said Miyasaka, referring to Beijing's export restrictions on the rare elements gallium and germanium used in chips. "With perovskite cells, the components can be made domestically."

Perovskite cells have been researched for more than a decade but initially couldn't match silicon cells in their efficiency at turning light into electricity, and tended to degrade in humid conditions.

So perovskite was used inside glass-covered silicon panels to boost efficiency in what are known as tandem cells, and governments in the U.S. and elsewhere have supported tandem-cell development.

Now, perovskite-only cells have caught up with or even surpassed silicon rivals, with conversion rates as high as 25% or more, U.S. Department of Energy data show. That compares with rates of around 18% to 22% for conventional commercial silicon panels.

The challenge now is making costs competitive with silicon cells and dealing with the humidity issue.

Developers of perovskite cells say their versatility sets them apart because they are light and flexible. The layer of crystalline perovskite is only one micron thick, resulting in a cell that is one-tenth the weight and one-twentieth the thickness of current solar cells. They can be installed on walls or curved surfaces and generate electricity under weak sunlight, even indoors.

"Let's say you live in an apartment and don't have your own roof. You can still put the perovskite cells on your balcony. Think of it as a household appliance," said Miyasaka, a professor at Toin University of Yokohama who previously worked at photo-film maker Fujifilm on solar technology.

Japanese Prime Minister Fumio Kishida has pledged to make the technology commercially viable in two years. Japan imports close to 90% of its energy since it closed most of its nuclear plants following the 2011 Fukushima nuclear disaster.

Kishida's target is ambitious, but Japanese engineers and officials are optimistic, citing recent technological advances.

Sekisui Chemical, a supplier to display makers, is tackling the moisture issue. It says it has developed sealants that allow its cells to last 10 years.

Sekisui is testing its perovskite cells outdoors on surfaces not suited for silicon panels, including on the wall of its Osaka headquarters. It is looking to place them in train stations and other public facilities.

The electricity-generating solar film is similar in look and feel to the film people used to put in cameras, except it is wider than 35-millimeter camera film.

Sekisui has produced test rolls of 30-centimeter film and plans commercial production in 2025, said Takeharu Morita, director of the project.

Proponents believe the production cost will eventually be lower because the cells don't require the energy-consuming heating process that is needed to make silicon cells.

The wider the film, the more difficult it becomes to create a thin, uniform layer of perovskite. For now, that means a larger sheet of perovskite cells is less efficient in generating power.

Some firms see that as a reason to avoid head-to-head competition with silicon panels initially, especially in large-scale generation.

EneCoat Technologies, a startup co-founded by a University of Kyoto professor, is eyeing the use of perovskite indoors and for smaller devices such as motion detectors that use little electricity.

The company has developed a portable carbon dioxide monitor powered by perovskite cells. It plans to start commercial production of cells for indoor use by the end of this year.

"We want to start off by aiming for places where silicon panels can't be used. We think that there's a bigger market there," said Tamotsu Horiuchi, EneCoat's chief technology officer.

Japanese companies are already feeling the heat from China. One company, DaZheng (Jiangsu) Micro Nano Technology, says it began commercial production of perovskite cells in 2022 and plans to increase capacity 10-fold.

Many engineers believe Japan still has a technological edge, since creating a uniform super-thin perovskite layer requires precise craftsmanship, a strength of Japanese manufacturing." [1]

1. China's Solar Dominance Faces Challenge From Ultrathin Cell. Nishiyama, George.  Wall Street Journal, Eastern edition; New York, N.Y.. 11 Jan 2024: B.1.