Stability and Degradation in Hybrid Perovskites: Is the Glass Half-Empty or Half-Full?

Methylammonium lead iodide (CH₃NH₃PbI₃) is an extensively used perovskite material with a remarkable potential for solar energy conversion. Despite its high photovoltaic efficiency, the material suffers from fast degradation when aging in atmospheric conditions and/or under sunlight. Here we review the principal degradation mechanisms of CH₃NH₃PbI₃, focusing on the thermodynamic, environmental and polymorphic parameters that impact the stability of the material. A critical analysis of the available data indicates that degradation under ambient conditions is a defect-generation process that is highly localized on surfaces and interfaces, while it is further enhanced above the tetragonal-cubic transition at ∼54 °C. Within this context, we discuss the conservative role of N₂ and propose strategies for the emergence of industrially viable hybrid photovoltaics.