The Best Is Yet To Come: New Tandem Silicon-Perovskite Solar Cell Sets Record

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Solar cells may seem like old hat by now, but there is still plenty of room for innovators to push costs down and pump efficiency up. From that perspective, the solar industry has only just begun to push fossil energy out of the global economy. A new record-setting silicon-perovksite solar cell is just one example of the renewable energy firepower emerging from the lab that may one day cross over to the marketplace.

The Long Road To A Perovskite Solar Cell

For those of you new to the topic, the semiconductor material silicon continues to dominate the commercial solar cell market, as it has since the early 2000s. Its relatively high cost is counterbalanced by its durability as well as its efficiency in converting sunlight to electricity.

On the prowl for less expensive solar conversion materials, researchers have hit upon the idea of using perovskites instead of silicon. Perovskites are synthetic crystalline materials based on the superior optical characteristics of the naturally occurring mineral perovskite. The discovery of perovskite dates back to the 19th century, but it wasn’t until the 1990s that researchers applied the structure to solar cells.

Synthetic perovskites are relatively inexpensive, and they could be a cost-cutting replacement for standard silicon solar cells. However, there is a catch. “Raw” synthetic perovskites are susceptible to humidity, and they decay when exposed to ambient air (see more CleanTechnica perovskite coverage here).

Because science loves a challenge, workarounds to the instability problem have been emerging from the lab and making their way to the solar market. That includes stabilizing perovskites with various other materials.

Piggybacking a perovskite solar cell onto a silicon cell is another approach. That sounds simple enough. Though, the devil is in the details. The challenge is to make the most of the cost-cutting opportunities offered by perovskites without impinging on the ability of the silicon component to deliver the solar conversion efficiency goods.

New Perovskite Solar Cell Leaps Shockley-Queisser Border

That brings us to the new solar cell record. On November 24, the Chinese solar company LONGi Green Energy Technology Co. announced a certified solar conversion efficiency record of 33.9% for its new silicon-perovskite tandem solar cell.

The 33.9% mark is significant because it marks the first time a silicon solar cell has surpassed the theoretical limit of 33.7% for the conversion efficiency of that particular type of cell. The conversion formula, called the Shockley-Queisser limit after the scientists who devised it in 1961, is based on the solar spectrum and the nature of the materials in a solar cell.

The 33.7% limit applies to solar cells made from one layer of semiconductor material. Far higher conversion efficiencies can be reached with multi-junction solar cells that deploy various combinations of materials, but multi-junction cells also tend to be far more expensive. Breaking a single junction solar cell through the Shockley-Queisser barrier offers up a potential win-win of low cost and high efficiency.

LONGi came close to the S-Q barrier earlier this year, with the announcement of 31.8% efficiency for a perovskite-silicon solar cell in May, followed by 33.5% in June. The new record of 33.9% might not last long either, since the company already seems to be setting its sights on the 43% theoretical limit for silicon-perovskite solar cells.

“The theoretical efficiency limit of crystalline silicon-perovskite tandem solar cells can reach 43%, and it is recognized as the mainstream technical solution to break through the efficiency limit of crystalline silicon single-junction cells,” LONGi noted in a press release last week. “The emergence of crystalline silicon-perovskite tandem technology has opened up a new track for the development of next-generation high-efficiency solar cell technology.”

The Green Hydrogen Connection

A new generation of low-cost, high efficiency solar cells has implications beyond simply lowering the cost of solar power. As LONGi notes, it also expands siting opportunities for solar arrays. Compared to less efficient solar cells, the new solar cell can absorb the same light from the same area but produce more electricity at less cost. As a corollary, the new cells could produce the same electricity in a smaller area with less light.

Among other applications, a new low-cost solar cell would help bring down the cost of green hydrogen, which is produced by applying electricity from renewable resources to water.

LONGi has already begun carving out a space in the global green hydrogen market. In the latest development, the company is bringing its solar technology to bear on green hydrogen production in Egypt.

On November 24, the news organization SolarQuarter reported on Egypt’s ambitious near-term solar energy and green hydrogen plans. “Looking ahead to 2035, the total installed capacity of green hydrogen projects commissioned in Egypt is expected to exceed 11.6GW, positioning Egypt at the forefront globally,” SolarQuarter noted.

Until green hydrogen emerged on the market, the primary source of hydrogen was natural gas. It still is, but the supply of green hydrogen is increasing with an assist from private sector investors and favorable government policies. That’s important because hydrogen is one of the gears that keep the modern industrial economy in motion. Fuel is just one use case. Many other sectors would benefit by a more sustainable hydrogen supply chain, including agriculture and food processing as well as metallurgy, medicines, and toiletries.

Low-Cost Solar Cells: Beyond Perovskites

Perovskites have stirred up a lot of excitement in the low-cost solar pot, but they are not the only game in town. Aside from introducing new solar cell technologies, the solar industry has been pushing down costs by scaling up. Improvements in supply chains and permitting systems have also factored in.

The Mercator Research Institute on Global Commons and Climate Change in Germany has been tracking the downward slide in the cost of solar power, and its latest report notes a decrease of 87% over the past 10 years alone.

As for the future, the Mercator researchers take stock of new energy-related technologies and systems to make the case for a global transition to renewable energy that is less costly and more feasible than previously predicted. Their study runs counter to conventional forecasts, which assume that expensive carbon capture and sequestration systems will be needed to offset the continued use of coal for power generation.

“Some calculations even suggest that the world’s entire energy consumption in 2050 could be completely and cost-effectively covered by solar technology and other renewables,” explains the lead author of the study, Felix Creutzig.

“This is an extremely optimistic scenario,” Creutzig adds, “But it illustrates that the future is open. Climate science, which provides policymakers with guidance in its scenario models, must reflect technical progress as closely as possible. Our study is intended to provide input for this.”

The intersection of solar energy with food systems — aka agrivoltaics — is another wrinkle to consider. If you have any thoughts about that, drop us a note in the comment thread.

Image: New world record for a tandem silicon-perovskite solar cell, courtesy of LONGi via prnewswire.

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