Investigating Root Causes of Gradual Power Loss During Outdoor Testing of Encapsulated Perovskite Modules Through Post-Mortem Failure Analysis

Metal halide perovskite (MHP) solar cells are an emerging thin-film photovoltaic (PV) technology projected to play an important role in the terawatt-level PV deployment. However, the lack of long-term operational stability in outdoor environments is currently a major hurdle and technological barrier to commercialization. Limited studies are available on outdoor testing of MHP cells and modules, and differences in cell/module encapsulation, architectures, chemistry, and fabrication processes further complicate our understanding of MHP outdoor reliability and associated degradation mechanisms. The Perovskite PV Accelerator for Commercializing Technology (PACT) center provides independent testing of mini-modules provided by the perovskite community. To date the PACT center has received and tested over 300 modules from 4 Universities and 5 industry providers. Here we present results of post-mortem analysis of encapsulated perovskite modules that underwent a gradual power loss throughout -200 days of field testing. Fully encapsulated perovskite modules exhibit longer field lifetimes compared to early module designs with an edge seal only, with the current T80 record of -140 days. Module scribe-lines were identified as potential weak spots resulting in resistive losses. We observe perovskite morphology deterioration near the scribes caused by chemical degradation. Accelerated stress-test protocols are being developed to build confidence in this new technology faster than the field alone. Initial results suggest that light and elevated temperature leads to similar degradation mechanisms as seen in the field. The role of the polymeric encapsulant on the degradation kinetics and mechanisms is going to be examined.