U.S. Scientists Unveil Methods for More Stable Perovskite Solar Panels

n the world of solar energy, metal halide perovskite (MHP) solar cells are getting a lot of praise for being highly efficient and cost-effective. However, a major hurdle stands in their path to widespread adoption: their thermomechanical stability. To tackle this issue, a team from Arizona State University has conducted an in-depth investigation into MHP modules and cells, aiming to identify the best strategies to boost their resilience to heat-related stress.

The Rising Star of Solar Technology

Perovskite solar cells are made from materials with a unique crystal structure, named after the mineral perovskite. Over the years, these cells have consistently broken their own efficiency records, which measure how much sunlight is converted into electricity. Starting at just a 3.8% rate in 2009, the most efficient solar cells made with perovskite materials have now reached an impressive 26.1%.

Source: National Renewable Energy Laboratory (NREL)

Perovskites absorb different light wavelengths compared to traditional silicon cells, which dominate 95% of today's solar market. When combined with silicon in tandem photovoltaic cells, they can capture even more of the solar spectrum, producing more electricity per cell.

There are other big benefits too. The raw materials for perovskite cells are relatively cheap, and they can be manufactured at lower temperatures than silicon-based cells, cutting down production costs. Plus, perovskite cells can be made on flexible and lightweight substrates, making them perfect for innovative applications like portable chargers, curved surfaces on buildings or vehicles, and even clothing.

Lastly, by tweaking their chemical composition, the optical and electronic properties of perovskites can be adjusted to optimize performance under different environmental conditions.

Understanding the Challenges

Despite their many advantages, perovskites still face hurdles that keep them from hitting the mainstream market. For instance, they are not very resistant to moisture, which can cause them to break down quickly when exposed to humid conditions. Also, the durability of perovskite solar cells isn't quite up to par with silicon-based ones yet, which could be a deal-breaker for long-term investors.

One of the biggest issues with perovskite solar cells is thermal stability. Unlike their silicon cousins that can take the heat and keep on ticking, perovskites start to falter under high temperatures. These materials start to degrade quickly at temperatures over 85 degrees Celsius—a mark that's not hard to hit in many places where PV systems get installed. This isn't just about them losing solar power efficiency over time; the heat can destroy the internal structure of the cells, which makes them unstable and results in a loss of their photovoltaic properties.

Insights from Recent Research

Scientists at Arizona State University have released a paper diving into how to toughen up metal halide perovskite modules and cells. The team believes the key to creating stable and the most efficient solar panels is understanding how different types of wear and tear—like, thermal, mechanical, and chemical—play off each other under the stresses of light, heat, and humidity.

Researchers have found that perovskite solar panels break down much faster in real-life conditions than they do in the controlled environment of a lab. Turns out, there isn’t much research into how these high efficiency PV panels handle different kinds of environmental stress, like changing temperatures and light conditions together. The team is shining a light on this overlooked issue, hoping to speed up the improvements and market readiness of perovskite solar solutions.

Addressing the Core Issues

The paper highlights that a major problem with perovskite solar cells is their poor stability when exposed to heat, which mainly appears in two serious issues. First, these cells have something called low fracture energy, meaning they aren't very good at stopping cracks from spreading. Second, the films in the solar cells are under a lot of stress because they and the base they're built on don't expand with heat in the same way. This mismatch puts a lot of tension on the films, creating defects that make the cells less effective.

To tackle these challenges, researchers have come up with a few effective methods:

• Boosting Fracture Energy: One way to make materials more durable is by strengthening the bonds between layers and enhancing the material's ability to stretch without breaking. For instance, treating the C60 layer with ozone before adding the tin-oxide (SnOx) layer has proven to significantly enhance the bond between these layers.
• Adding Compressive Stress: By adding certain types of polymers to MHP films, scientists can introduce compressive stress that works against the stretching forces that usually cause damage. This method has proven to keep things stable, making the materials last longer and degrade less.
• Enhancing Surface Protection: Using 2-dimensional perovskites to protect the surface can improve the stability and toughness of the cells by strengthening the mechanical properties of the absorber layer.

To push the stability and reliability of metal halide perovskites to new heights, scientists have introduced a few more improvement strategies. One idea is to use inert materials like carbon for the electrodes instead of silver. This change helps prevent degradation from ions moving around, which in turn, makes the devices more durable.

Another improvement involves adding scaffold structures within the MHPs. These structures provide mechanical support, which not only aids in better crystallization but also reduces the likelihood of defects. Finally, replacing traditional fullerene-based materials in the electron transport layers with alternatives like SnOx combined with polymer layers could offer a more robust and long-lasting option.

Realistic Testing for Commercial Viability

The researchers emphasize the importance of more effective testing methods for perovskite solar modules, as current lab tests don't fully mimic the real-world stresses these efficient solar panels face. They suggest testing the devices by cycling them through various temperatures while exposing them to continuous light. This method would more closely mirror actual conditions and give a clearer picture of the modules' long-term stability and reliability.

The team recommends that the materials need to reach at least 1 J/m² in toughness. This ensures that the devices can endure the assembly and packaging stages without breaking down. Meeting this standard helps prevent the layers from coming apart and extends the life of the panel.

Conclusion

The work done by scientists at Arizona State University is a big leap toward making perovskite solar technologies better for everyday use. By addressing the key challenges related to film stresses, bonding between layers, and the impact of weather and other environmental factors, the research provides a plan for advancing perovskite solar technologies to be more stable and long-lasting.

Source:

https://www.nature.com/articles/s43246-024-00515-2

https://www.nature.com/articles/s41467-023-40585-3