An international team of researchers applied π-conjugated terpyridine Lewis-base molecules as a perovskite absorber passivating treatment in a study that determined it could be applied in high concentration. Used in prototype perovskite solar cells, it reportedly improved passivation durability without diminishing performance.
The perovskite durability-enhancing treatment based on π-conjugated terpyridine Lewis-base molecules was used in perovskite solar cells that reportedly achieved 25.24% power conversion efficiency and retained 90% of the initial performance after 2,664 hours of light exposure.
The results demonstrated that the treatment works at high concentrations, which is typically needed to passivate surface defects over time, and that it could be applied without damaging the perovskite or diminishing the performance of the solar cells made with it, overcoming a problem identified in past experiments.
“We have discovered a π-conjugated terpyridine molecule with a concentration-independent passivation effect, a property that allows us to treat the surface of perovskite at high concentrations without affecting the device efficiency, whereas for most passivators, high concentrations tend to deteriorate the device performance,” corresponding author, Rui Wang, told pv magazine.
The group said that their technology enabled high-concentration passivation without reducing device performance, which considerably improves passivation durability. “The concentration independence enables excess-concentration surface passivation, which enhances passivation durability as the excess passivation molecules interact with newly formed defects as devices degrade,” it explained.
The team noted stability tests showed 90% of initial efficiency after 2,664 hours of light exposure, and 82% after 2,976 hours of heating. The experimental devices had a short circuit current density of 25.97 mA/cm2, an open circuit voltage of 1.19 V, and a fill factor of 81.65%.
The research was reported in “Enhanced Passivation Durability in Perovskite Solar Cells via Concentration-Independent Passivators” published in Joule- The contributing scientists were from China-based Westlake University, Shangyu Institute of Semiconductor Materials, Zhejiang University, and Fudan University, along with US-based University of California, Los Angeles, and Lawrence Berkeley National Laboratory.
In a separate research, meanwhile, scientists from Westlake University and Zhejiang University published “Protocol for fabricating long-lasting passivated perovskite solar cells,” released in STAR Protocols, providing the information required to reproduce the results.
“The most interesting aspect of the protocol described is the detailed description of a procedure for passivating the surface defects with a unique terpyridine molecule whose passivation effect is independent of concentration, thus greatly improving the durability of the passivation,” said Westlake's Wang.
Details are provided on how to fabricate n-i-p structured terpyridine-passivated solar cells in a nitrogen atmosphere, including the electron transport layer via chemical bath deposition, the perovskite light absorbing layer via a two-step method, how to passivate the surface defects with excess terpyridine ligands, and how to conduct stability characterization.
The protocol also outlines the theoretical calculation simulations, time-of-flight secondary ion mass spectrometry, and grazing incidence X-ray diffraction to verify how the molecules accumulate on the surface of the perovskite.
By following the instructions, it is possible to obtain long-passivated and high-efficiency perovskite devices, according to the researchers.
The team stated that the protocol may also be suitable for fabricating perovskite solar cells with other perovskite absorbers, such as “bromide and iodide mixed perovskites or with other different self-aggregated passivator agents.”
Looking ahead, Wang said that his team will continue to address “some of the problems with defect passivation engineering, such as reproducibility and generalizability.”
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