Solar cells, which produce electricity from sunlight, are already contributing to lower fossil fuel emissions in numerous countries around the world. Recently, energy engineers have been exploring alternatives to silicon to create solar cells that are more efficient, long-lasting, and cost-effective.
These materials include perovskites, especially halide perovskites, which have a distinctive ABX₃ crystal structure and contain halides—compounds formed from a halogen element combined with a metal or positively charged ion.
Halide perovskites are highly effective at absorbing light and transporting charge carriers, which allows solar cells made from them to achieve high power conversion efficiencies (PCEs). However, they are generally much less stable than traditional silicon solar cells, meaning their performance tends to deteriorate quickly over time.
Enhancing Halide Perovskite Solar Cell Stability
To address this issue, researchers at Purdue University, Emory University, and other institutions have developed a new approach aimed at enhancing the operational stability of halide perovskite solar cells.
Their proposed method, described in a paper in Nature Energy, involves improving solar cells using specially designed ionic liquids—salts that remain liquid at low temperatures and interact strongly with certain materials.
“Our team focuses on organic synthesis, hybrid perovskite crystal growth, and device engineering,” said Letian Dou, the paper’s senior author, in an interview with Tech Xplore.
He added, “An industry partner asked us to create new additives to enhance the long-term stability of the devices. We reviewed existing research and were inspired by a previous study that used ionic liquids as additives. However, that study only used simple, commercially available ionic liquids and didn’t carefully design the molecular structures.”
Building on previous research, Dou and his team aimed to create new molecules that interact strongly with perovskites, minimizing small defects and slowing their degradation over time. Importantly, the ionic liquids they developed proved more effective than those used in earlier studies at stabilizing perovskite solar cells.
Novel Ionic Liquids that Improve Solar Cell Performance
Halide perovskite solar cells are typically comprised of three layers. These include two so-called interface layers and the active perovskite layer sandwiched between them.
“It is very important to minimize the defects in the perovskite layer, as well as the two interfaces (top and bottom of the perovskite layer),” explained Dou. “Despite widespread efforts aimed at improving the top interface by coating an additional surface passivation layer, few efforts have been made for bulk defect passivation and bottom (buried) interface.”
The most promising ionic liquid designed by the researchers, dubbed MEM-MIM-CI, binds strongly to positively charged lead ions in perovskites, while also filling halide vacancies (i.e., sites at which halide ions are missing). Dou and his colleagues added this liquid to a perovskite material, then used it to develop a solar cell and assessed its stability.
“These new ionic liquids, when incorporated into the perovskite precursor, create an intermediate phase during crystallization,” explained Dou.
“This intermediate phase slows the crystallization process and encourages the formation of larger perovskite grains with fewer defects. We also observed that the ionic liquid tends to accumulate at the bottom interface, which helps reduce defect formation.”
Testing Improved Perovskite Solar Cells Under Extreme Conditions
The researchers then evaluated the performance of solar cells made from their improved perovskite material under extreme conditions. They first tested the devices at temperatures between 65–80°C and under intense light exposure (equivalent to full sunlight, or 1-Sun irradiation).
“Our sponsor later raised the standards, asking us to examine how the devices would degrade under even more severe conditions—at least 90°C while exposed to light,” said Dr. Wenzhan Xu, the study’s first author.
“Consequently, we tested our devices under these more extreme conditions and showed that they maintain 90% of their initial performance for more than 1,500 hours under continuous 1-Sun illumination at 90°C in open-circuit mode—conditions that are more severe than those usually applied by other researchers.”
Advancing the Implementation of Perovskite Solar Cells
The preliminary findings by Dou, Xu, and their team demonstrate that carefully engineered ionic liquids can enhance the stability of halide perovskite solar cells. These results may encourage other researchers to develop similar ionic liquids for incorporation into perovskite precursor solutions.
“The materials we worked with are simple to synthesize and can be produced at scale,” said Dou. “This approach could potentially enable the industrial-scale production of large-area perovskite solar cell devices, as ionic liquids allow scalable, solution-based deposition methods such as blade coating.”
“Moreover, we discovered that these ionic liquids can improve both the efficiency and stability of wide-bandgap and lead-free perovskite systems, highlighting the broad applicability of this approach for tandem solar cell technologies.”
Dou and his team are planning further research to enhance the stability of perovskite-based solar cells. They are working on designing more effective molecules that could boost the durability of these devices under real-world conditions.
Dou added, “We also seek to gain deeper insights into the basic mechanisms of ionic liquid–perovskite interactions through advanced spectroscopy and imaging methods.”
“We are open to partnerships with industry collaborators, and the patent for this technology is available for licensing. We hope this innovation will help advance the commercialization and broader adoption of stable perovskite solar cells.”
Read the original article on: Tech Xplore
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