Perovskite-based multijunction solar cells are rapidly approaching the stage of commercial deployment, exhibiting extraordinary advancements in their energy conversion efficiencies over the past five years. For example, the most efficient two-terminal configuration that has been developed to date is a tandem structure combining perovskite materials with silicon (Si). Despite these impressive efficiency gains, the long-term reliability and stability of these solar devices remain significant concerns.

One of the primary reasons for this uncertainty is the relatively brief period since the inception and development of perovskite-based multijunction solar cells. This short timeframe poses substantial challenges for conducting long-term, decade-spanning reliability tests, primarily due to the inherent time constraints associated with such extensive evaluations. Additionally, there is a notable lack of established accelerated aging protocols, which are essential for predicting the long-term performance and durability of these devices. This gap exists because the fundamental failure mechanisms of perovskite-based multijunction solar cells are not yet fully understood, making it difficult to develop standardized testing methods that can reliably simulate prolonged operational conditions.

In the upcoming presentation, I will elaborate on our recent research findings that investigate the behavior of perovskite cells when integrated into multijunction configurations. First, I will explore how defects at the nanometric scale can initiate and propagate degradation within the solar cells (starting from single-junctions), ultimately impacting their overall performance and longevity. Furthermore, I will discuss the various strategies we have developed to mitigate these nanometric defects, thereby enhancing the stability and reliability of the devices.[1,2]

Beyond the microscopic level, I will also address the effects observed at larger scales, such as the micrometer (µm) and centimeter (cm) levels. For instance, the choice of texturing applied to the silicon cells plays a crucial role in determining both the performance and stability of the solar cells, however by adjusting fabrication parameters, µm-sized textures can be covered without performance loss. [3]  Moreover, I will highlight how precise control of passivation over various length scales has enabled us to fabricate wafer-scale tandem devices with high performance [4]. Finally, we extend our reach beyond tandem devices and I will showcase our latest developments in perovskite-perovskite-Si triple junction solar cells. [5]