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Simulating the flexible materials needed to advance renewable energy

FAMU-FSU Engineering uses Simcenter Multimech to power the advancement of perovskite solar cells

Simulating the flexible materials needed to advance renewable energy
An example of roll-to-roll printed solar cells being created. Image Credit: Commonwealth Scientific and Industrial Research Organization.

FAMU-FSU College of Engineering

The FAMU-FSU College of Engineering, established by the Florida Legislature in 1982, is the joint engineering school for Florida A&M and Florida State universities, the only shared college of engineering in the nation.

https://eng.famu.fsu.edu/

本社:
Tallahassee, Florida, United States
製品:
Simcenter 3D Solutions
業種:
エネルギー / ユーティリティ

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Using Simcenter Multimech to elevate the development of the next generation of flexible solar cells has marked a transformative leap.
Dr. Melissa Davis, Postdoctoral Researcher, National Renewable Energy Laboratory

Leveraging solar power

Solar power is vital to ensure a sustainable future for this planet. A total of 173,000 terawatts of solar energy strikes the Earth continuously – about 10,000 times the world’s total energy use per year. This means in just one hour the Earth’s surface receives enough sunlight to supply the annual electricity needs of every human being on Earth. So if that energy can be
harnessed, we could enjoy completely renewable power for as long as our sun keeps burning – currently estimated at a few billion years.

But harnessing that energy is the tricky part. In 2019, just over 2 percent of global electricity came from solar power because the current cost of manufacturing and installing solar panels is still substantial.

A major factor of the high cost is related to the manufacturing process of silicon solar cells, the most commonly used material. Silicon devices require an expensive, energy-intensive, multistep manufacturing process. To promote wider use of solar power, much less expensive solar panels need to be developed that are just as effective at harnessing the sun’s energy.

With a collaboration between Dr. Melissa Davis, Dr. Zhibin Yu and Dr. Rebekah Sweat at the FAMU-FSU College of Engineering, the joint college for Florida A&M and Florida State Universities, the researchers have found a way to overcome these challenges and drive the next generation of flexible perovskite solar cells, at its High-Performance Materials Institute (HPMI).

She used the Simcenter™ Multimech™ platform from Siemens Digital Industries Software to create a virtual model that she could run simulations on. Analyzing the results enabled her to understand the cause of the cracking and find areas of mechanical weakness. She also ran simulations with different parameters for elements such as material selection, manufacturing thickness and mechanical bending performance. These tests allowed her to try out different combinations in the virtual environment and immediately discard the ones that would not work. Then by refining the simulations, she was able to find the most promising configurations and manufacture them for full physical testing.

“Using Simcenter Multimech to elevate the development of the next generation of flexible solar cells has marked a transformative leap,” says Davis, who is now a postdoctoral researcher at the National Renewable Energy Laboratory. “With Simcenter Multimech the material microstructure can be precisely digitalized and real-life performance is captured, which enabled us to conduct in-depth analyses of cracking phenomena. The capability of Simcenter Multimech to simulate diverse materials seamlessly and pinpoint a crucial interlayer to prevent cracking played a pivotal role. This approach empowered us to remotely explore multiple possibilities before crafting the most efficient solutions.”

The solar cells of the future

Perovskite solar cells have been identified as the potential game changer to make solar energy affordable. Perovskites are crystalline structures found in nature, such as calcium titanate. One subset – metal halide perovskites – has been found to have excellent semiconducting properties, which make them suitable for solar cells. Additionally, this material is much more adaptable than traditional silicon solar cells, which make the manufacturing and installation process much quicker and cheaper. Additionally, their flexibility means they have the potential to be manufactured via roll-to-roll printing, similar to
a newspaper printing assembly line. This technique prints each sequential layer quickly to form the complete device that can achieve a high production rate.

Although the material is more flexible, bending still leads to cracking, which decreases the solar cell’s efficiency and lifespan. Although scientists have been researching ways to improve the resistance of perovskite solar cells to cracking, the time and cost required to investigate
their mechanical degradation has hampered efforts.

Material simulation

Researching and building perovskite solar cells with many different materials and then testing their resistance to cracking and degradation is time-consuming and costly. So instead Davis set out to create a digital twin to simulate performance before manufacturing test samples.

In previous simulations, perovskite crystals were modeled with hexagonal shapes, but for this study Davis wanted to improve this to give a true representation of the crystals. She used a MATLAB algorithm to convert captured scanning electron microscope (SEM) images from grayscale to binary that enable digitalization. With the Harris-Stephens algorithm, differences between pixels were detected to establish the grain boundaries between crystals. This process allowed for a fully digitalized image from a SEM still, which further enabled updating the crystal geometry to include grain boundaries. With this new information, simulation coupons could be created with an accurate representation of the crystal structure. By using this technique, the researchers could use simulation to accurately study the mechanisms of failure.

Mechanical data to assess mechanical performance

Davis explains that mechanical research of perovskites is split into two fields – one focusing on mechanical stresses due to expansion and contraction, and one focusing on mechanical stresses due to physical forces such as bending. Davis says she focused on the latter because it was the least investigated.

“The commonly used method to report mechanical resiliency is to state the efficiency of devices before and after the bending of cells over a stated radius,” explains Davis. “But this uses electrical data to describe mechanical performance while we feel that it’s critical to use
mechanical data to assess mechanical performance. This allows us to view stresses and strains within the layers instead of viewing the devices as a unit.”

A known mechanical weak point of perovskite solar cells is the indium tin oxide (ITO) layer. ITO has excellent electrical properties but has been proven brittle, leading to cracks when bent. So Davis focused on finding a replacement material that would have the comparable electrical properties but be much more flexible and resistant to cracking and degradation.

Using Simcenter Multimech, which is part of the Siemens Xcelerator business platform of software, hardware and services, Davis created simulations with different material configurations. One simulation had three layers – polyethylene terephthalate (PET) at the bottom, ITO in the middle and perovskite on top, while the other was created without the ITO layer.

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Bending without breaking

Simcenter Multimech was used to subject the models to a three-point bend and data was collected on the resulting cracks and stresses. This clearly showed that the model with the ITO layer had a different reaction to bending. The ITO model had significant cracking in the perovskite crystals, while this was minimal in the non-ITO model. Instead, cracking was limited to the perovskite grain boundaries, proving that the simulation was accurate in predicting the performance of the ITO material.

"Now we have a robust simulation method with Simcenter Multimech to predict the mechanical deformation of perovskite films and we can utilize it in the search for a better material to replace ITO,” says Davis. “With this tool, we can quickly test varying compositions to determine mechanical properties much faster and cheaper than with previous physical methods.

“We can also use the same system to build the model that includes all layers of a perovskite solar cell. This allows us to connect mechanical degradation with the efficiencies of complete devices.”

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Solar power for everyone

Now that simulation is reducing the time and expense of research, it seems like it’s only a matter of time before perovskite cells make an impact on the solar power industry.

“Perovskite solar cells unlock a more widespread use of solar energy with their reduced costs,” says Davis. “This will grow the market for both energy companies and individual households. By reducing the cost barrier to renewable energy with technologies such as this, the transition from nonrenewable sources can be accelerated.”

Davis also believes the flexibility of future perovskite solar cells will lead to all sorts of innovative uses of solar energy. “Imagine going to the beach with a towel that has a solar panel built into it. You could easily keep your cell phone and other devices charged all day long. Or instead of boats using sails purely to capture wind to propel them, the sails could also harvest solar energy to power the engine without any fuel.”

Thanks to this groundbreaking analysis of perovskite solar cells, including the work done by Davis at the FAMU-FSU College of Engineering, scientists have a new method of improving solar cells faster and cheaper than ever before.

With Simcenter Multimech the material microstructure can be precisely digitalized and real-life performance is captured, which enabled us to conduct in-depth analyses of cracking phenomena.
Dr. Melissa Davis, Postdoctoral Researcher , National Renewable Energy Laboratory