An ultra-thin protective coating appears to be enough to protect a perovskite solar cell from the damaging effects of space and harden it against environmental factors on Earth, according to newly published research from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL).
Funded by the U.S. Department of Defense’s Operational Energy Capability Improvement Fund (OECIF), the NREL research was conducted for the Air Force Research Laboratory (AFRL) to develop low-cost, innovative energy sources to power the armed forces around the world .
The research is the latest effort to determine the effectiveness of perovskites for use in space applications, where it would be exposed to protons, alpha particles, atomic oxygen and other stressors. The opportunity to use perovskites to generate power in space is enticing as they provide a cheaper and lightweight option to other technologies with the potential to achieve efficiencies comparable to current space PV technologies.
As on Earth, perovskite solar cells must have suitable durability. However, the environment in space is significantly different. While Earth’s greatest challenges are related to weather, perovskites in space must deal with the problems posed by radiation bombardment and extreme temperature swings. Perovskites are showing signs of better tolerance to radiation than many other solar cells, but much testing remains to be done.
Researchers last year simulations performed to demonstrate how exposure to space radiation would affect perovskites. They determined that the next-generation technology would work in space, but pointed out the need to encapsulate the cell in some way to provide additional protection.
In the follow-up study, Ahmad Kirmani, lead author of the latest Nature Energy paper, simulations said a micron-thick layer of silicon oxide would preserve efficiency and extend the life of perovskite solar cells in space. By comparison, the micron-thick layer is about 100 times thinner than a typical human hair.
Kirmani said the silicon oxide layer can reduce the weight of conventional radiation barriers used for other solar cells by more than 99% and serves as a first step toward designing lightweight and low-cost packaging for perovskites.
High-energy protons travel through perovskite solar cells without doing much damage. However, low-energy protons are more abundant in space and do more damage to perovskite cells by knocking atoms into place and causing efficiency levels to steadily decline. The lower energy protons interact with matter much more easily and the addition of the silicon oxide layer protected the perovskite from damage even by the low energy protons.
“We thought it would be impossible for the silica to provide protection against fully penetrating long-range particles such as the high-energy protons and alpha particles,” Kirmani said. “However, the oxide layer turned out to be a surprisingly good barrier against that as well.”
The results are detailed in the paper “Metal oxide barrier layers for photovoltaics on Earth and in space.The co-authors are David Ostrowski, Kaitlyn VanSant, Rosemary Bramante, Karen Heinselman, Jinhui Tong, Bart Stevens, William Nemeth, Kai Zhu, and Joseph Luther, of NREL; and several key collaborators working with the team from the University of North Texas and the University of Oklahoma. VanSant is uniquely positioned to be a postdoctoral researcher at NASA conducting research at NREL.
Exposure to a stream of low-energy protons caused unprotected perovskite solar cells to lose only about 15% of their initial efficiency, the researchers found. A greater concentration of particles destroyed the cells, while the protected perovskites demonstrated what the scientists described as “remarkable resilience.” With the simple barrier, the cells showed no damage.
In addition to making the cells more resilient in space, the researchers also tested how the barrier could prove beneficial in more conventional applications. They then exposed the perovskite solar cells to an uncontrolled environment of moisture and temperature for several days to mimic storage conditions. The protected cells maintained their initial efficiency of 19%, while the unprotected cells showed significant degradation, from 19.4% to 10.8%. The oxide layer also provided protection when other perovskite compositions, which are typically more sensitive to moisture, were exposed to water.
Further, the perovskite solar cells were subjected to a test chamber where they were bombarded with ultraviolet photons, similar to the environment in low Earth orbit. The photons interacted with oxygen to create atomic oxygen. The unprotected cells were destroyed after eight minutes. The protected cells maintained their initial efficiency after 20 minutes and showed only a slight decrease after 30 minutes.
The simulations and experiments showed that by reducing the damage from radiation, the life of the shielded solar cells used in Earth’s orbits and deep space would be extended from months to years.
“The energy conversion efficiency and operational stability of perovskite solar cells have been the two main areas of concern for the community so far,” he said. “We’ve made a lot of progress and I think we’re well on the way to reaching the targets needed for industrialization. However, to really make this market entry possible, packaging is the next target.”
Because perovskite solar cells can be deposited on a flexible substrate, the emerging technology, in combination with the silicon oxide protective layer, allows its use for various terrestrial applications, such as powering drones.
NREL is the U.S. Department of Energy’s premier national laboratory for renewable energy and energy efficiency research and development. NREL is operated for DOE by the Alliance for Sustainable Energy LLC.
Thanks to NREL
Related:
Scientists decide how to prove perovskite panels for space power
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