Accelerated Lifetime Testing of Organic-Inorganic Perovskite Solar Cells Encapsulated by Polyisobutylene

Metal halide perovskite solar cells (PSCs) have undergone rapid progress. However, unstable performance caused by sensitivity to environmental moisture and high temperature is a major impediment to commercialization of PSCs. In the present work, a low-temperature, glass-glass encapsulation technique using high performance polyisobutylene (PIB) as the moisture barrier is investigated on planar glass/FTO/TiO₂/FAPbI₃/PTAA/gold perovskite solar cells. PIB was applied as either an edge seal or blanket layer. Electrical connections to the encapsulated PSCs were provided by either the FTO or Au layers. Results of a "calcium test" demonstrated that a PIB edge-seal effectively prevents moisture ingress. A shelf life test was performed and the PIB-sealed PSC was stable for at least 200 days. Damp heat and thermal cycling tests, in compliance with IEC61215:2016, were used to evaluate different encapsulation methods. Current-voltage measurements were performed regularly under simulated AM1.5G sunlight to monitor changes in PCE. The best results we have achieved to date maintained the initial efficiency after 540 h of damp heat testing and 200 thermal cycles. To the best of the authors' knowledge, these are among the best damp heat and thermal cycle test results for perovskite solar cells published to date. Given the modest performance of the cells (8% averaged from forward and reverse scans) especially with the more challenging FAPbI₃ perovskite material tested in this work, it is envisaged that better stability results can be further achieved when higher performance perovskite solar cells are encapsulated using the PIB packaging techniques developed in this work. We propose that heat rather than moisture was the main cause of our PSC degradation. Furthermore, we propose that preventing the escape of volatile decomposition products from the perovskite solar cell materials is the key for stability. PIB encapsulation is a very promising packaging solution for perovskite solar cells, given its demonstrated effectiveness, ease of application, low application temperature, and low cost.