Singh, RojaHu, HangFeeney, ThomasDiercks, AlexanderLaufer, FelixLi, YangDuong, TheSchackmar, FabianNejand, Bahram A.Paetzold, Ulrich W.2026-01-312026-01-311944-8244PubMed:38751205ORCID:/0000-0002-1298-4743/work/203982623https://hdl.handle.net/1885/733805141The long-term stability of perovskite solar cells (PSCs) remains a bottleneck for commercialization. While studies on the stoichiometry and morphology of PSCs with regard to performance are prevalent, understanding the influence of these factors on their 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, postdegradation 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-) ions 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. In summary, this work emphasizes the importance of reporting stability under different stress conditions, coupled with postdegradation and dark recovery analyses of PSCs to better understand the complexities of perovskite instability under real-life conditions such as expected during outdoor operation.Financial support from the Initiating and Networking funding of the Helmholtz Association (Project Zeitenwende and the Solar Technology Acceleration Platform (Solar TAP)), the program-oriented funding IV of the Helmholtz Association (Materials and Technologies for the Energy Transition; Topic 1: Photovoltaics and Wind Energy, Code: 38.01.04), the German Federal Ministry for Economic Affairs and Climate Action (BMWK) through the projects 27Plus6 (03EE1056B) and SHAPE (03EE1123A), and the Karlsruhe School of Optics and Photonics (KSOP) is gratefully acknowledged.13en©2024 The authorsdegradationlightlong-term stabilityquenchingstoichiometrytemperature2024-05-1510.1021/acsami.4c0435085193485503