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Composition dictates octahedral tilt and photostability in halide perovskites

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Stranks, Samuel 
Orr, Kieran 
Iqbal, Affan 
Nagane, Satyawan 
Ferrer Orri, Jordi 


Halide perovskites are excellent candidate materials for use in solar cell, LED, and detector 12 devices, in part because their composition can be tuned to achieve ideal optoelectronic 13 properties. Empirical efficiency optimisation has led the field towards compositions rich in FA 14 (formamidinium) on the A-site and I on the X-site, with additional small amounts of MA 15 (methylammonium) or Cs A-site cations and Br X-site anions. However, it is not clear how and 16 why the specific compositions of alloyed, i.e. mixed component, halide perovskites relate to 17 photo-stability of the materials. Here, we combine synchrotron grazing incidence wide-angle 18 x-ray scattering, photoluminescence, high-resolution scanning electron diffraction 19 measurements and theoretical modelling to reveal the links between material structure and 20 photostability. Namely, we find that increased octahedral titling leads to improved photo-21 stability that is correlated with lower densities of performance-harming hexagonal polytype 22 impurities. Our results uncover the structural signatures underpinning photo-stability and can 23 therefore be used to make targeted changes to halide perovskites, bettering the commercial 24 prospects of technologies based on these materials.



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Advanced Materials

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EPSRC (EP/V012932/1)
Engineering and Physical Sciences Research Council (EP/R023980/1)
Royal Society (UF150033)
Horizon Europe UKRI Underwrite MSCA (EP/X025756/1)
Engineering and Physical Sciences Research Council (EP/S030638/1)
EPSRC (1948691)