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Composition Dictates Octahedral Tilt and Photostability in Halide Perovskites.

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


Publication status: Published

Funder: Gonville and Caius College, Cambridge

Funder: Cambridge Philosophical Society; doi:

Funder: British Spanish Society

Funder: Sir Richard Stapley Educational Trust; doi:

Funder: Rank Prize Fund

Funder: Ernest Oppenheimer Fund

Funder: Schmidt Science Fellowships

Funder: Taiwan Cambridge Scholarship

Funder: D.M.P. Foundation

Funder: St John's College, Cambridge

Funder: Royal Academy of Engineering; doi:

Funder: Diamond Light Source; doi:


X‐ray diffraction, density functional theory, electron microscopy, perovskite, photovoltaics

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Adv Mater

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Engineering and Physical Sciences Research Council (EP/L015978/1)
European Research Council (756962)
Engineering and Physical Sciences Research Council (EP/R023980/1)
Engineering and Physical Sciences Research Council (EP/S030638/1)
EPSRC (EP/V012932/1)