The development of stable perovskite solar cells (PSCs) is crucial for their breakthrough in the photovoltaic (PV) market. While PSCs offer high power conversion efficiencies (PCEs), low-cost and straightforward fabrication, their stability is lower than traditional silicon PVs. PSCs are highly susceptible to degradation caused by intrinsic factors, such as the structural and chemical stability of the materials used, as well as by external factors like moisture, oxygen, light, and temperature. Hermetic encapsulation, offered by laser-assisted glass frit sealing, provides effective protection against the external environment, with proven stability enhancement of n-i-p and HTM-free structures.[1, 2] However, light-induced degradation remains a challenge, particularly in triple mesoscopic structures where mesoporous TiO₂ (ETL) accelerates degradation under UV light and oxygen. Replacing this mesoporous TiO₂ layer with non-photocatalytic alternatives, incorporating UV filters, or using insensitive to photocatalytic degradation perovskites are some pathways to mitigate the UV-driven degradation.[3] However, perovskite degradation can also be induced by the atmosphere inside the hermetic cell cavity due to the presence of moisture and/or oxygen. Most of the studies that investigate the light stability of PSCs under controlled atmospheres have also not been conducted in encapsulated cells, as they would be in actual working conditions.[4, 5]

The present study addresses the challenges of achieving long-term stability in perovskite solar devices by assessing the impact of laser-assisted glass frit encapsulation under different atmospheres – non-controlled (air), CO₂, and N₂ - on the stability of 5-AVAxMA1-xPbI3 perovskite films and HTM-free solar cells to light. Using a hermetic chamber filled with a controlled atmosphere and equipped with a glass lid, both films and cells were encapsulated via the laser-assisted glass frit process. The encapsulated devices were subjected to continuous 1-sun illumination at 45 °C for more than 1000 hours of light exposure. After monitoring the absorbance of the perovskite films over the exposure period in conjunction with Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis of perovskite films with different aging conditions, i.e. fresh, aged in dark and in light, the results show that films glass encapsulated under a nitrogen atmosphere exhibited the best stability while the films encapsulated under non-controlled atmosphere (air) suffered extensive degradation. Moreover, these results are aligned with the photovoltaic performance of PSCs exposed to the same aging conditions. Further investigation is necessary to assess the role of the carbon counter electrode in the stability of the cells, which is related to the ability of this carbon layer to adsorb moisture and reactive gases. Overall, these findings highlight the importance of laser-assisted glass frit encapsulation as an effective strategy for improving the stability and performance of perovskites. Furthermore, the study emphasizes the importance of using a controlled atmosphere during the encapsulation process.