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Figure 1 : CrystalStructure of theprototype AMX3perovskite emphasizingthe corner sharing

connectivity of the[MX!

"# units an$ the

A' cation function as structuraltemplates an$ their shape( sizean$ charge $istri&ution arecrucial factors for the sta&ilizationof the perovskite structure)

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*$eal cu&ic archetype structure[m#+#m , 1-.o !

l structure of hali$e perovskites follo/ing the se0uential phase transitions fromote$ α to the $istorte$ β MA2&*3)

 he perovskite un$ergo a

series of structuralchanges upon applicationof e+ternal stimuli

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 he 4an$ gap

• 5e6ne$ &y the or&ital overlap &et/een the metal an$ the hali$e ions

•   A cations $o not $irectly contri&ute to the electronic properties

• 5ecreases /ith increasing atomic mass

• 4an$ gap $ecreases /ith increasing atomic mass

• 7o/ever in the case of AMX3 Sn have narro/er &an$ gaps than the heavi

  2& materials• Sn , 11-)81 u 1)% 1)" ev• 2& , %.8)% u 1)"9 1)8ev

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α phase un$istorte$ perovskiteβ phase 1st phase transitionγ  phase # %n$ phase transitionδ phase non perovskite structure

A cation in$irect contri&ution steric Coulum&ic interactions ;ctahe$ral tilting

changes in the electronic stucture &an$gap energetics