As perovskites have moved toward commercialization, the importance of mechanical reliability is receiving a significant increase in attention. Perovskites are susceptible to delamination and fracture from processing, handling, and operational conditions. We describe the mechanical properties of state-of-the-art perovskite solar cells, which have incorporated various compositions and microstructures to improve performance and chemical stability. The aim of this work was to understand how composition affected perovskite mechanical integrity and determine design criteria to increase cohesion and reliability toward the development of module-scale devices.
We report on recent studies characterizing the intrinsic mechanical integrity of perovskite compositions and fully explore the role of various cation combinations, additives, and microstructure on perovskite cohesion. Adding cations to the perovskite decreased mechanical integrity, largely due to smaller grain sizes and increased concentration of PbI2. Microindentation hardness testing was performed to estimate the fracture toughness of single-crystal perovskite, and the results indicated perovskites are inherently fragile, even in the absence of grain boundaries and defects. Introducing plastically deformable cations led to a modest improvement in cohesion, and the most robust architecture was observed by infusing perovskite into a porous TiO2/ZrO2/C layer that provided extrinsic reinforcement to mechanical and environmental stressors. These developments fulfill design for reliability criteria and are the type of device architectures that could transition perovskites from lab-scale to commercialization.
The mechanically fragile nature of perovskites is a property that, if ignored, could inhibit the long-term success of perovskite solar cells as a viable solar technology. Designing robust cells with long operational lifetimes—in addition to high-efficiency—must be a primary focus for perovskites to be commercially realized.