Seasonality in perovskite solar cells

Insights are reported from a 4-year outdoor study in Berlin using encapsulated p–i–n perovskite solar cells with the structure ITO | 2PACz | Cs0.15FA0.85PbI2.55Br0.45 (bandgap of 1.65 eV) | C60 | SnO2 | 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.