| Work Detail |
Researchers at the US National Renewable Energy Laboratory (NREL) develop a method that produces efficient and stable perovskite solar power.
A new approach to making perovskite solar cells developed by NREL researchers addresses previous problems and leads to devices with high efficiency and excellent stability.
The development of highly stable and efficient perovskites based on a mixture rich in bromine and iodine is considered essential for the creation of tandem solar cells. However, the separation problems of the two elements under operating conditions of the solar cell, such as light and heat, limit the voltage of the device and its operational stability. This problem is often aggravated by the easy defect formation associated with rapid crystallization of bromine-rich perovskite with antisolvent processes.
“This new growth approach can significantly suppress phase segregation,” says Kai Zhu, NREL principal scientist, project principal investigator, and lead author of the new paper “ Compositional texture engineering for highly stable wide-bandgap perovskite solar cells. ” compositional texture for highly stable broadband perovskite solar cells). His NREL co-authors are Qi Jiang, Jinhui Tong, Rebecca Scheidt, Amy Louks, Robert Tirawat, Axel Palmstrom, Matthew Hautzinger, Steven Harvey, Steve Johnston, Laura Schelhas, Bryon Larson, Emily Warren, Matthew Beard, and Joseph Berry. Other participating researchers belong to the University of Toledo.
The new method solved the problem of separating the two elements and produced a broadband solar cell with an efficiency greater than 20% and a photovoltage of 1.33 volts. Efficiency hardly changed during 1,100 hours of continuous high-temperature operation. Ultimately, the researchers achieved an all-perovskite tandem cell that achieved 27.1% efficiency with a high photovoltage of 2.2 volts and good operating stability.
In the tandem cell, the narrow bandgap layer is deposited on top of the wide bandgap layer. The difference in bands makes it possible to capture a greater part of the solar spectrum and convert it into electricity.
The new method builds on work that Zhu and his colleagues published earlier this year, which inverted the typical perovskite cell. Using this inverted architectural structure allowed the researchers to increase both efficiency and stability and easily integrate tandem solar cells. In the end they got a perovskite solar cell with an efficiency of 24% that retains 87% of the production after 100 days.
In the recent research study, the NREL-led group used that same architecture in that they used an antisolvent applied to crystallizing chemicals to create a uniform perovskite film. Then they went a step further, and the new approach was based on what is known as gas quenching, in which a stream of nitrogen was blown over the chemicals. The result was a perovskite film with better structural and optoelectronic properties.
The previous anti-solvent method allowed crystals to grow rapidly and evenly within the perovskite film, crowding each other and giving rise to defects where the grain boundaries meet. The new gas-quenching process, applied to high-bromine perovskites, forces the crystals to grow together, tightly packed from top to bottom. The researchers found that this significantly reduces defects. The top-down growth method forms a gradient structure, with more bromine near the top and less in the bulk of the cell. The researchers report that the gas quench method was also statistically more reproducible than the anti-solvent method.
The researchers also tested argon and air as drying gases with similar results, indicating that the gas quenching method is a general way to improve the performance of broadband perovskite solar cells.
The new growth method demonstrated the potential of high-performance all-perovskite tandem devices and prompted the development of other perovskite-based tandem architectures, such as those incorporating silicon. |
