International research groups are breaking barriers in solar cell efficiency, leveraging the properties of perovskite to surpass traditional silicon limitations.
Solar energy has long been touted as the key to a sustainable future, but its potential has been hampered by the inefficiency of solar cells. However, ground-breaking research on perovskite-based solar cells by several international teams is bringing the promise of significantly improved efficiency in harnessing solar power.
Silicon, the traditional material for solar cells, has a theoretical maximum efficiency of just 29.4% due to its narrow frequency band compatibility with sunlight.
Looking to surpass this limit, the two research groups—one from Germany's Helmholtz-Zentrum Berlin für Materialien und Energie GmbH and the other from Switzerland's École Polytechnique Fédérale de Lausanne—have focused their efforts on layering silicon with other materials capable of converting light of different frequencies into electricity.
The material of choice? Perovskite, a crystal made from a mixture of titanium and calcium.
Perovskite is a type of crystal, created from a mixture of titanium and calcium. This structure shows immense potential for improving solar cell efficiency, making perovskite solar cells a hot topic in energy circles. The crux of the matter lies in overcoming electron reabsorption, a hurdle that has traditionally hampered perovskite's effectiveness.
In essence, perovskites work by capturing and converting sunlight into electricity, just like conventional silicon solar cells. However, these cells can utilize a broader range of frequencies due to the unique properties of perovskite, leading to improved energy conversion rates.
So far, perovskite’s promise has been hampered by the tendency of some electrons to be reabsorbed into the crystal, inhibiting its electricity-generating capabilities.
To tackle this issue, each group adopted a unique approach.
The team at Helmholtz-Zentrum Berlin infused a pre-existing layer of perovskite with a liquid known as piperazinium iodide. This resulted in a highly efficient solar cell with an energy conversion rate of 32.5%.
Meanwhile, their counterparts at École Polytechnique Fédérale de Lausanne prepared a silicon layer with precursor chemicals, subsequently inducing a reaction that created a flawless perovskite coating, resulting in solar cells with an efficiency of 31.2%.
To achieve a balance between cost and efficiency, tandem photovoltaic devices (two-layer) are designed such that the top layer absorbs high-energy photons and converts them to electricity while remaining transparent to other wavelengths. The lower layer absorbs lower energy photons.
Silicon, having peak absorption towards the red end of the spectrum, is suitable for the lower layer. Perovskites are considered good candidates for the top layer because of their structure, variety, and potentially inexpensive source materials. The peak wavelength absorbed by the resulting crystal can be adjusted by carefully selecting the raw materials for perovskites.
According to Interesting Engineering, the Chinese solar cell manufacturer LONGi has also reported energy conversion rates as high as 33.5% for their own solar cells. Besides that, there had been successful demonstrations of tandem perovskite/silicon cells, but their efficiencies haven't exceeded what silicon can achieve independently.
Most exciting of all, Ars Technica writer John Timmer reported that theoretical calculations offer that these efficiencies can be further developed to reach as high as 45%. However, it is unknown whether longer-lasting perovskites are compatible with high efficiencies in a tandem configuration.
A major issue with perovskites is that their crystals are not stable and can degrade back into raw materials in a matter of weeks to months. The devices reported in the studies had short lifetimes, with the most stable one retaining 80% of its initial efficiency after just 66 hours of exposure to sunlight, and the other maintaining the same level of efficiency for 347 hours.
While these solar cells have demonstrated impressive results on a smaller scale, overcoming the challenge of commercial viability is the next hurdle for researchers. Current tandem perovskite solar cells are much smaller than commercial silicon cells, and their production may prove costlier.
Yet, with the solar market expanding rapidly and the potential energy yield justifying the initial investment, experts are optimistic that these hurdles can be overcome. As research progresses, we are bound to witness increased interest from perovskite solar cell manufacturers looking to capitalize on these promising advancements.
Interestingly, it could be as early as 2024 by the time we see a version of these cells produced at commercial scale. As reported by PV Mag and The Independent, the German researchers at Helmholtz Zentrum Berlin teamed up with the South Korean firm Qcell on a four-year embarkment last November to establish a pilot line for the industrial production of these cells.
Shortly after the team shared its work and had those results certified by the Department of Energy, Qcell announced its parent company would invest $100 million towards a pilot production line to commercialize its own tandem perovskite solar cells by next year.
Elsewhere, a China-based startup called Renshine Solar is also on the brink of launching the production of its own perovskite solar panels. Founded by researchers from Nanjing University, the researchers claim Renshine can produce perovskites at half the cost and with 50% higher efficiency than traditional silicon cells.
To spearhead the commercialization of perovskite cells, Professor Tan Hairen founded Renshine Solar and has successfully secured a government contract to establish a production line in Jiangsu province commencing this summer. The resulting perovskite solar panels are designed to be deployed on rooftops, walls, and electric vehicles to enhance their range.
"Perovskite cells' raw materials are not only abundant but also inexpensive, making them 5% of the cost of conventional solar cells," Professor Tan said. "Given their simplified production process and the potential for single-factory production, even after including other production factors, the overall cost is just half that of conventional silicon cells."
Notably, the perovskite solar cells have demonstrated promising endurance, and have maintained over 90% of their initial performance even after 600 hours of continuous operation. This is the attribute that the company believes qualifies them for commercial use.
By September, the factory is projected to ramp up a capacity of 150 megawatts, as reported by the South China Morning Post. While the initial market will be roofs, walls, and EVs, the next-gen solar cells are anticipated to find applications across sectors as broad as integrated building panels to space-based power generation.
Though perovskite solar panels are not yet widely available, the increased efficiency and potential for reducing green energy production costs make them a highly promising prospect. While only tested on smaller-scale solar cells, the Swiss and German teams' research points to a future where enhanced efficiency could make solar power an even greater power source.
Consider how the global solar market has expanded at a significant annual rate of 24% over the past decade. Because solar installation in the U.S. tends to double every 18 months, in six years we could see solar capacity reach as high as 80% of the grid. And since researchers found the levelized cost of energy has averaged 15%-24% declines every time supply doubles, costs could drop dramatically by the end of the decade.
However, much more remains to be done. To stave off catastrophic climate change scenarios, a global consensus of experts state solar capacity must grow to 75TW of total capacity by 2050.
As John Timmer writes for Ars Technica, only a 25-33% of the total cost of building a solar farm is accounted for by solar panels. The remaining costs are related to additional hardware, financing, installation, permitting, and other factors - so if you're going to install all that expensive hardware, it makes sense to focus on improving the efficiency of the panels as high as you can.
Tandem perovskite cells, if not perovskite cells on their own, are set to play an increasingly crucial role in achieving this goal.
As researchers continue to optimize perovskite's crystal structure and further boost solar energy efficiency, we can expect a surge in the contribution of solar power to global electricity production when these cells hit the market. This all sounds very exciting - now we just need energy storage to pick up the pace!
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