Investigating the Mechanism behind the Degradation of Cu-Based n-i-p-Type PSC Modules

Perovskite solar cell (PSCs) modules using cost-effective copper electrodes encounter significant challenges in long-term operational stability, limiting their commercial viability. We systematically investigate the degradation behavior of n-i-p structure PSCs modules under continuous illumination. The P3 interconnection region is identified as the primary site of failure, where localized corrosion initiates and propagates during operation. Using optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX), we reveal a pronounced redistribution of Cu and iodide species near the P3 region in aged devices. Bias-dependent studies (-2 to +4 V) show that forward bias significantly accelerates degradation, while thermal stress alone does not induce corrosion, indicating a field-driven mechanism. We propose that lateral migration of iodide ions toward the P3 region, followed by electrochemical reactions with Cu, leads to the formation of corrosive products and ultimately electrode failure. A thin bismuth (Bi) interlayer between MoO₃ and Cu effectively suppresses ion migration and interfacial reactions. As a result, the modified modules retain over 90% of their initial performance after 400 h of continuous illumination, compared to rapid failure in control devices. This work provides direct insight into bias-induced degradation in PSC modules and establishes an effective interfacial strategy for enhancing the stability of Cu-based electrodes.