In the last 10 years, perovskite solar cells have gained significant interest as a promising candidate for advanced photovoltaic technology. In order to succeed in the commercial market, this novel solar technology must either surpass silicon solar cell technology in terms of the levelized cost of power or target specialized industries with somewhat higher costs where conventional solar technologies are not viable. This typically requires solar cells with long term stability, industrially scaled production techniques, high efficiency, and, if desired, the ability to fabricate on flexible substrates.
Architecture of Perovskite solar cells
The conventional “nip“ and inverted “pin“ forms of perovskite solar cells are the most common device architectures. Both architectures exhibit efficiencies of 25%, exceeding the efficiency of research solar cells made from polycrystalline silicon.
i. Inverted perovskite solar cells
Inverted perovskite solar cells exhibit enhanced stability at high temperatures. However, these cells mostly rely on fullerenes (C60) or C60-derivatives, which have some problems by nature, like not sticking well to other surfaces, which can cause layers to separate. Replacing the C60 layer is necessary for the purposes of scaling up and commercializing.
ii. Regular perovskite solar cells
The instability at high temperatures limits the great potential of the regular “nip“ perovskite solar cell design. Typically, it incorporates an organic small-molecule hole transport layer called 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]−9,9′-spirobifluorene (Spiro-MeOTAD). The high cost of spiro-MeOTAD is a potential obstacle to the widespread commercialization of perovskite cells that rely on this material. We base this assumption on the retail price, which is freely available for purchases of small quantities, typically a few grams. Nevertheless, the projected retail price falls below 50 USD per gram for kilogram purchases, as per several supplier price estimates in December 2023. Spiro-MeOTAD purity will be reduced, and larger order quantities will result in further reductions in retail costs.
Scientist’s recent contribution to Perovskite solar cells
MIT scientists have improved the stability of Spiro-MeOTAD in perovskite solar cells, allowing them to be tested at high temperatures for over 1,400 hours without losing effectiveness. This breakthrough has led to a solar cell with a remarkable efficiency of 24.2%, despite quick degradation, demonstrating the potential of Spiro-MeOTAD in the development of solar energy.
Optimized Perovskite solar cells durability at elevated temperature
Dr. Matthias J. Grotevent and Nobel Prize laureate Moungi G. Bawendi’s research demonstrated that their unique technology can produce a stable Spiro-MeOTAD material that remained stable even after 1,400 hours of testing under continuous one-sun illumination, a crucial feature for solar panel applications.
Key findings of the Research
Their research demonstrates the potential benefits of this innovative approach. Researchers discovered that Spiro units showed a considerable increase in electrical conductivity, reaching values that were orders of magnitude greater, even with a low doping concentration of 1%.
Benefits of the Material used in optimized Perovskite solar cells
The material blend’s raised glass transition temperature, exceeding 115 degrees Celsius, enhances the thermal characteristics of the solar cell, making it suitable for use in locations with the highest temperatures. The study team believes that additional research could increase the stability of the Spiro unit, which is currently only present in a solar cell with a 6% efficiency, in order to achieve a 24% efficiency.
Too expensive to commercialize the Optimized Perovskite solar cells
The study found that Spiro is currently quite expensive, selling for $334 per gram on the internet. However, the researchers are anticipating a significant price drop when buying in bulk, up to kilogram quantities. The end result could be a price of $30 or even $3 per gram. Dr. Grotevent provided an estimate of approximately 0.33 grams of Spiro for a standard-size solar panel when PV Magazine USA inquired about the material’s cost. This estimate was based on an assumed layer thickness of approximately 120 nanometers. Approximately $1.06 of the total module cost would go toward the material cost of solar panels with an efficiency of more than 20%, which is less than $0.003 per watt.
Limitations of optimized Perovskite solar cells
Scientists are now investigating three primary methods for implementing perovskites, which have had limited utilization thus far. The initial approach entails placing perovskites on top of silicon in the solar cell, a technology that has gained much interest due to its exceptional efficiency, as demonstrated by Longi’s groundbreaking 34.6% perovskite-silicon tandem solar cell. Second, GCL Perovskites is testing a method that combines the outputs of perovskite and silicon solar panels by building virtually complete perovskite solar panels and then overlaying them. The third method uses independent perovskite panels that do not require silicon. The 1 MW China Three Gorges solar power station exemplifies this.
Conclusion
In recent years, perovskite solar cells have gained attention as a promising candidate for advanced photovoltaic technology. To succeed in the commercial market, these cells must outperform silicon solar cell technology in terms of levelized power costs or target specialized industries with higher costs. Researchers at MIT have made Spiro-MeOTAD more stable in perovskite solar cells, resulting in a solar cell with a remarkable efficiency of 24.2%.
The material blend has an elevated glass transition temperature exceeding 115 °C, enabling improved thermal characteristics and the potential for 24% efficiency. However, Spiro’s cost is currently too high to commercialize. Researchers are investigating three primary methods for implementing perovskite solar cells: placing perovskites on top of silicon, combining perovskite and silicon solar panels’ outputs, and using independent perovskite panels without silicon.
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