Researchers from the Chinese Academy of Sciences (CAS) have analyzed the degradation behavior of copper (Cu) electrodes in perovskite solar cells and found that pronounced side corrosion contributes significantly to device deterioration.
The scientists explained that, despite their cost advantages compared to gold (Au) and solber (Ag) counterparts, Cu electrodes suffer from energy-level mismatch, halide-induced corrosion, and moisture-related degradation, and said that recent strategies, including buffer layers, alloying, and molecular interlayers, have improved Cu electrode stability, particularly in conventional n-i-p perovskite solar cell architectures.
Their analysis involved a pervoskite cell typ integrating a molybdenum trioxide (MoO3) buffer layer. Initial device optimization showed that introducing the layer improved hole extraction and enabled the cell to achieve efficiencies comparable to Ag-based devices. However, operational stability tests revealed rapid performance losses due to localized side corrosion and increased interfacial resistance.
Microscopy analysis confirmed that corrosion originates from the Cu edges and gradually extends inward, damaging both the electrode and underlying perovskite layer. Time-resolved photoluminescence, transient photocurrent, and transient photovoltage measurements showed increased defect formation and enhanced non-radiative recombination in degraded regions.
The degradation mechanism was attributed to light-induced perovskite decomposition, which releases iodide ions that migrate toward the Cu electrode and react to form corrosive copper-iodide (CuI) compounds. Further analysis confirmed significant iodine accumulation near the aged Cu electrode.
In order to address these challenges, the researchers introduced a thin bismuth (Bi) interlayer between MoO3 and Cu, creating a protective barrier against iodine diffusion and Cu corrosion, and Bi-based devices demonstrated improved operational stability, retaining a significantly higher proportion of their initial efficiency after prolonged illumination.
The protective effect of Bi was linked to its stronger resistance to halide reactions and its ability to prevent CuI formation at the interface.
Further analysis showed that the indium tin oxide (ITO)/Cu overlap region acts as an electrical protection zone by improving charge extraction and reducing ion migration.
In contrast, regions without ITO coverage experienced charge accumulation, promoting iodide migration and electrode corrosion. Light-beam-induced current measurements confirmed that areas with efficient carrier extraction were less vulnerable to degradation.
The side corrosion of the Cu electrode on the MoO3 surface was only found on the edges, but the ITO and Cu electrode overlap area remains unaffected,” the scientists stated. “This side corrosion was initially confirmed by peeling off the electrode and further examined by a microscope and the Scanning Electron Microscopy (SEM).”
“The results indicate that no side corrosion occurs when only the active area is illuminated,” they concluded. “The result shows that Bi works as a corrosion-resistant material that is not only beneficial for improving device stability and performance but also beneficial for suppressing the Cu electrode corrosion.”
Their findings are available in the paper “Unexpected side Cu corrosion at Cu/MoO3 interface in Cu-based n-i-p type perovskite solar cells,” published in Materials Design.
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