Researchers Develop Practical Perovskite Solar Cells With Peak Efficiencies of 24.5%

Recently, researchers have managed to develop a manufacturing process that combines 2D and 3D structures to maximise the efficiency of perovskite solar cells. Why is perovskite considered the future material for solar panels, what did the researchers demonstrate, and do they present an environmental concern?

Why are perovskite solar cells so desperately desired?

Of all solar cell technologies, none have received the same amount of media attention as those based on Perovskite structures. Researchers working on this technology area have managed to raise the efficiency of such solar cells from a mere few percent in 2001 to 25% in 2021. With efficiencies already exceeding those of standard silicon solar panels, Perovskite solar cells will likely enter the mass market before the decade’s end. But even if they are a few percent more efficient than solar cells, why are they so sought after by the engineering community?

If Perovskite solar cells can be made practical for mass production, they will undoubtedly solve numerous energy challenges faced by solar cells and the wider renewable energy market in general. The most important factor of Perovskite materials is that they are significantly cheaper than solar cells as they use readily available materials such as lead. As such, the cost of electricity from such solar panels would help reduce energy costs while also providing an economical solution for replacing fossil fuels. (One figure puts the cost of perovskite solar cells at £0.18 per square foot compared to £4 per square foot for traditional solar cells). 

The second major advantage of perovskite materials is that they are deposited as thin films, and these films can often be deposited in liquid form, which is much easier to deal with compared to the need for +1000˚C for silicon. At the same time, these thin films can be deposited onto uneven surfaces, which introduces new possibilities for integrating energy harvesting capabilities into enclosures, packaging, and even clothes. Furthermore, semi-transparent solar cells can sacrifice efficiency for transparency and be used on windows (some perovskite cells can be used to absorb infrared only while leaving visible light). 

Thirdly, perovskite layers as thin as 500nm can be mostly opaque, meaning that the full efficiency of a panel is realised in thin films. As a result, perovskite solar cells would be much thinner and lighter than traditional silicon technologies, and this could help provide aircraft with energy harvesting capabilities while having minimal effect on the weight. 

Researchers demonstrate that combined perovskite solar cell show longevity

For all the benefits of perovskite solar cells, there is a reason why they still remain in laboratory environments; they are often vulnerable to changing environmental conditions and can degrade quickly. A large bulky solar panel may have lower efficiency than the latest perovskite solar cell, but at least it will last for at least 20 years in direct sunlight with minimal degradation.

However, researchers have recently demonstrated a new perovskite solar cell that has demonstrated significant resilience to strong light and changing conditions. The new solar panel, developed by researchers from Rice University, has been shown to have an efficiency of 24.5% and experienced less than 1% degradation even after full exposure to equivalent sunlight (100W per square meter) for 2000 hours. Furthermore, the test was done at a temperature of 55˚C with a relative humidity of 65%, which is relatively extreme considering that few places on the planet experience 55˚C.

In order to achieve this design, the researchers combined both 2D and 3D versions of an identical perovskite material to maximise efficiency (by absorbing both infrared and visible light) while making the manufacturing processes feasible for commercial purposes. To create individual perovskite layers, researchers had to use a solvent to deposit solutions, but while this is perfectly fine for planar 2D devices, 3D structures would dissolve in said solvent (thereby destroying the structure). As such, the researchers turned to simulations and data analysis to try and identify solvents that could be used to create a 2D planar device while leaving the 3D substrate alone.

To be specific, the researchers were able to take advantage of the solvent’s dielectric constant and Gutmann donor number to produce pure 2D halide stacks on top of the underlying 3D structures. Thus, the 3D to 2D transition structure allows for the solar cell to first absorb visible light in the top half while absorbing infrared on the bottom half. 

Do perovskite solar cells present environmental challenges?

While perovskite may seem like the solution to the green energy challenge, those wanting to roll out the technology as soon as possible should think very carefully before doing so. Even though the materials used by perovskite materials are widely available, they are also often toxic especially lead. If such panels are thrown away at landfills, these compounds can leech into the surrounding ground and contaminate soil and underground water sources. 

Researchers are actively looking to replace these compounds with less harmful alternatives, but little progress has been made in this area. As such, the first mass-produced perovskite solar cells will likely be based on lead compounds, and this will introduce numerous challenges for engineers. Even though the RoHS directive in the EU outlaws the use of lead in consumer electronics products, it doesn’t prevent lead from being used in all products, and the drive for green energy could allow governments to make exceptions for perovskite solar cells. Thus, the world would be trading its own environmental problem for another; cooling down the earth or polluting the ground. By contrast, energy sources such as gas are extremely clean for the environment, with the only real pollutant being CO2. 

So, what do we do? Do we push out lead-containing solar cells that can be deployed cheaply, or do we stick with current energy solutions and hope that we can find something better for the environment?