Danger in the Dark: Stability of Perovskite Solar Cells with Varied Stoichiometries and Morphologies Stressed at Various Conditions

Long-term stability of perovskite solar cells (PSCs) remains a bottleneck for commercialization. While studies of PSCs stoichiometry and morphology with regard to performance are prevalent, understanding of these factors influence on long-term stability is lacking. In this work, we evaluate the impact of stoichiometry and morphology on the long-term stability of cesium formamidinium based PSCs. We demonstrate that the lead iodide (PbI2) to formamidinium iodide (FAI) ratio influences stability under various stress factors (elevated temperature and light). A high molar ratio (PbI2/FAI >1.1) in the perovskite precursor displays drastic degradation under ISOS-L1 (100 mW/cm2, 25 °C, maximum power point tracking) conditions. However, post-degradation analysis contradicts these results. Devices with PbI2/FAI ≤1.1 are stable under light but intermittent current density-voltage characterizations indicate that device performance decreases during storage in the dark. Migration of iodide (I-) to the electron transport layer (ETL) and iodine vacancies (VI-+) to the hole transport layer (HTL) forms localized shunts in the absorber layer. Pinhole formation, surrounded by FA+ rich regions, explains the extent of damage in comparably aged films. ... mehrIn summary, this work emphasizes the importance of reporting stability under different stress conditions, coupled with post degradation and dark recovery analysis of PSCs to better understand the complexities of perovskite instability under real-life conditions such as expected during outdoor operation.