Seasonality in Perovskite Solar Cells: Insights from 4 Years of Outdoor Data

Abstract Insights are reported from a 4‐year outdoor study in Berlin using encapsulated p–i–n perovskite solar cells with the structure ITO | 2PACz | Cs 0.15 FA 0.85 PbI 2.55 Br 0.45 (bandgap of 1.65 eV) | C 60 | SnO 2 | Cu. Peak summer performance showed little to no degradation during the first two summers and only ≈2% absolute drop in outdoor power conversion efficiency from the first to fourth summer. Despite good stability, the devices exhibit significant seasonality, with winter performance up to 30% lower than in summer during the first year, increasing with aging. The factors contributing to this seasonality are separated into four categories: I) solar spectrum, II) device temperature, III) maximum power point tracking losses, and IV) metastability effects. Among these, metastability – particularly light‐soaking behavior – is the largest contributing factor that sets perovskite technology apart from conventional photovoltaics. It was found that in cold, low‐light winter conditions, voltage gains from light‐soaking remain unsaturated, leading to reduced performance. Full saturation requires more than 24 h of continuous illumination, indicating that device performance depends on more than a single diurnal cycle. This comprehensive analysis highlights the complexity of seasonal behavior and the importance of long‐term, real‐world testing for accurate forecasting of perovskite photovoltaic energy yield.