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20, reported that replacing iodide by bromide in the mixed perovskite results in a blue shift of the absorption edge, which makes these mixed cation/anion perovskites outstandingly more stable under photo-illumination. Efforts have also been put forth to alleviate the effect of moisture and other factors on the stability of perovskite solar cells by partial substitution of I with Br ions 15, device architecture 16, 17, coating the perovskite cells with a water-proof fluorinated polymer 18 and deposition methods 19. Further, compositional engineering 12, 13 and the use of cation cascade technique 14 has been recently demonstrated to reduce the material photo-instability. For instance, by the assistance of cross-linking additives, material instability can be addressed to a certain extent 11.
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So far, several solutions have been proposed to make the perovskite materials more stable. When exposed to moisture, perovskite materials tend to hydrolyze, which results in their disintegration back into their precursors and finally irretrievable degradation of the perovskite structures. Various environmental factors including moisture, ultraviolet light and thermal stress, play a key role in the instability of perovskite materials 8, 9, 10.
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Even though the progress of perovskite solar cells (PSCs) has gone from operating under unstable liquid electrolytes far to solid state hole-transporting materials (HTMs) 7, a proper understanding of degradation mechanisms for perovskite materials and their relevant solutions still need to be explored. Chemical instability of organic-inorganic hybrid lead halide perovskites limits their performance and durability in various applications such as solar cells 1, 2, photo-assisted water splitting 3, 4, solid-oxide fuel cells 5, 6 etc.