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Hybrid perovskites are recently developed photoactive semiconductors that hold great promise for next-generation solar cells, with devices incorporating them reaching certified efficiencies as high as 22.1%. [1] This high performance is coupled with a relative low cost, as perovskites comprise earth-abundant elements that are amenable to deposition from the solution-state by scalable, inexpensive printing processes. [2] Recent work has focused on improving their long-term stability with significant progress being reported in encapsulation techniques and scalability with the production of modulescale devices (100 cm 2 ) exhibiting efficiencies of over 11%. [3][4][5][6] These developments have resulted in efforts to commercialize perovskite solar cells; however, there is still concern over the potential to achieve the 25-year service lifetimes necessary to make perovskites a disruptive technology.Photoactive perovskite semiconductors are highly tunable, with numerous inorganic and organic cations readily incorporated to modify optoelectronic properties. However, despite the importance of device reliability and long service lifetimes, the effects of various cations on the mechanical properties of perovskites are largely overlooked. In this study, the cohesion energy of perovskites containing various cation combinations of methylammonium, formamidinium, cesium, butylammonium, and 5-aminovaleric acid is reported. A trade-off is observed between the mechanical integrity and the efficiency of perovskite devices. High efficiency devices exhibit decreased cohesion, which is attributed to reduced grain sizes with the inclusion of additional cations and PbI 2 additives. Microindentation hardness testing is 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. The devices found to have the highest fracture energies are perovskites infiltrated into a porous TiO 2 /ZrO 2 /C triple layer, which provide extrinsic reinforcement and shielding for enhanced mechanical and chemical stability. Perovskite Solar CellsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

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