  My study is about Halide Perovskites (HaPs) and focuses the fundamental
structural, chemical and dielectric properties of HaPs in reference to their
PV-related properties.
  * I present my main research model: HaP single-crystals - their growth and
characterization;
  * I start by exploring the bond nature of HaPs using Nanoindentation and
Solid-State NMR techniques.
  * I explore the 'deformation potential' of the structure and show that its
low and positive value in HaPs strongly suggests a pronounced 'defect
tolerance'.
  * I explore the scattering mechanism of charges in the soft and highly
polarizable system such as HaPs, and show that its low mobility (relative to
other heteropolar systems) is fundamental and cannot be improved. I also show
that a positive 'deformation potential' (so the valence band is 'anti-bonding',
where a system should promote 'defect-tolerance') is something that is common
to other highly polarizable systems, such as AgX, and Pb-chalcogenides.
  * I explore the chemistry of the system and show that HaPs can easily break
to constituents, but also easily be made by the same constituents, suggesting a
low activation energy for annealing process to take care even at RT. This RT
annealing can promote 'self-healing' at ~second to ~minute time-scale, which we
clearly observe. We find 'entropic-stabilization' to be very important in
'self-healing' processes of that kind.
  * I explore the importance of symmetry breaking in the HaP structure, which
can induce a polar - and thus Ferroelectric - structure. We conclude that
Ferroelectricity is not a fundamental property of HaPs, since it doesn't exist
in MAPbBr3, but only in MAPbI3 - as proven unambiguously - and what is present
in MAPbI3 is in doubt important for photovoltaics, when using them at RT or
above.
  Due to compression, if you find a low-quality figure you want- please email
me.
