Researchers at the Massachusetts Institute of Technology (MIT) have achieved a significant breakthrough in stabilizing a key component of perovskite solar cells. They have developed a method to synthesize Spiro-MeOTAD, a crucial material for charge transport, without using noble metals. This development led to the creation of a solar cell with an impressive 24.2% efficiency, although it experienced rapid degradation.
The research, led by Dr. Matthias J. Grotevent and Nobel Prize laureate Moungi G. Bawendi, demonstrated that their new method can produce a Spiro-MeOTAD material that remains stable even after 1,400 hours of testing at elevated temperatures (85°C) under continuous one-sun illumination. This durability is critical for materials exposed to the high temperatures and humidity typical of solar panel environments.
Their study, titled “Additive-free oxidized Spiro-MeOTAD hole transport layer significantly improves thermal solar cell stability,” underscores the potential of this new method. The researchers discovered that “even at low doping concentrations of 1%,” Spiro units could increase their electrical conductivity by orders of magnitude.
One of the key benefits of the material blend is its high glass transition temperature, which is above 115°C. This allows the solar cell to exhibit enhanced thermal properties, making it more suitable for use in high-temperature environments.
In all of this, the research team says that while the thermally stable Spiro unit is only in a solar cell that reaches 6% efficiency, they see a path via future research to stabilize the 24% efficiency solar cell.
According to the study, Spiro is currently an expensive material, priced online at $334 per gram. However, the researchers predict that the price could drop significantly with bulk orders reaching kilogram levels, potentially falling to $30 per gram or even $3/gram. When asked about the material’s cost by pv magazine USA, Dr. Grotevent estimated that a full-sized solar panel would require approximately 0.33 grams of Spiro, assuming a layer thickness of about 120 nanometers. This would result in a material cost of less than $0.003 per watt for a solar panel with an efficiency of over 20%, adding about $1.06 to the overall cost of the module.
Researchers are exploring three main approaches to deploying perovskites, which have so far seen limited use. The first method involves stacking perovskites atop silicon within the solar cell, a technique that has gained significant attention for its high efficiency, exemplified by Longi’s record-setting 34.6% perovskite-silicon tandem solar cell. The second approach, currently undergoing testing by GCL Perovskites, involves constructing nearly complete perovskite solar panels and layering them over similarly complete silicon solar panels to combine their outputs. The third approach features standalone perovskite panels without silicon, as demonstrated by the 1 MW China Three Gorges solar power facility.
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