The role of MAPbI 3 hydrate in triple mesoscopic stack minimodules: the key to elongating outdoor lifespan

Abstract

Outdoor-tested TMS minimodules exhibit reversible, humidity-induced V OC gains linked to hydrate formation. Real-time V OC monitoring enables predictive maintenance, boosting long-term durability alongside advanced encapsulation strategies. Despite their promising performance and low-cost fabrication, perovskite solar cells (PSCs) face significant commercialization challenges due to their environmental instability, limiting their long-term durability. While encapsulation strategies improve stability, no existing solution demonstrates PSCs can last at timescales comparable to market-dominant silicon photovoltaics. This study explores an alternative approach: complementing effective encapsulation with maintenance actions. To enable such interventions, it is essential to understand how environmental factors influence device performance in real-world conditions. To do so, we fabricated triple mesoscopic stack (TMS) MAPbI 3 perovskite solar cells and mini-modules, encapsulated them with different materials, and deployed them for outdoor testing in North Yorkshire, UK, across different seasons. We observed that under the high relative humidity (RH) experienced on site, devices showcased an increase in open-circuit voltage ( V OC ), temporarily enhancing power output. Laboratory experiments using XRD confirmed this V OC -to-RH relationship to be driven by the reversible formation and dissolution of MAPbI 3 monohydrate, which facilitated charge extraction at the perovskite/carbon interface. While prolonged exposure led to degradation, partial recovery was achievable through temperature- or vacuum-induced water removal. Notably, Parylene-C encapsulation effectively prevented irreversible degradation under high humidity and temperature conditions. These findings reveal that V OC and short-circuit current density ( J SC ) variations can serve as in situ early indicators of reversible hydration-induced degradation, enabling preventative maintenance before power loss occurs. These findings support circular economy principles and, alongside advances in encapsulation, can increase PSC durability, bringing the technology closer to commercial viability.