Stability Assessment of Large-Area (1 cm ² ) Organic Solar Cells via Correlated Electronic, Morphological, and Interface-Induced Instability

Stability under ambient conditions and scalability of the device architecture are key challenges limiting the commercial deployment of organic solar cells (OSCs). Here, OSCs with active areas of 0.06 cm 2 and 1 cm 2 were fabricated entirely under open-air conditions, and their operational stability and degradation pathways were systematically examined. Both devices underwent accelerated photoaging and photothermal aging for 100 h in ambient conditions. Photoaging was carried out under continuous LED illumination (100 mW/cm 2 ), while photothermal aging combined continuous illumination with an elevated temperature of 85 °C, following standard accelerated stability protocols. Spatially resolved degradation was investigated through pixel-by-pixel performance mapping across the full device area by using raster-scan external quantum efficiency, transient photovoltage/current measurements, atomic force microscopy (AFM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiling for fresh and aged devices. This multimodal approach enabled a direct correlation between local electronic losses, morphological evolution, and interface-induced instability, particularly in large-area devices. Small-area devices exhibited an initial power conversion efficiency (PCE) of 14.51% and retained approximately 90–80% of their initial efficiency, along with 97–94% retention of other photovoltaic parameters after 100 h of aging. In contrast, large-area (1 cm 2 ) lab-scale devices, with an initial PCE of 12.18%, maintained only about 75–65% of their original performance. AFM and TOF-SIMS analyses revealed that photodegradation at the MoO 3 /Ag interface induces metal migration and bubble formation within the active layer, leading to localized trap-assisted recombination losses, consistent with a shortened recombination lifetime (TPV) and slower charge extraction (TPC). Thermal stress further amplified these effects, accelerating performance decay. Overall, these results underscore the importance of thermally stable interfaces, optimized device architectures, and effective encapsulation strategies for achieving scalable and durable OSC technologies.