Material CsPbBr₃ (cesium lead bromide) was studied here. It is widely used in solar cells, LEDs.
At high temperatures (>100K), transport shifts to a band-like motion, where charge carriers move smoothly.
At low temperatures (<100K), charge carriers move by hopping transport (jumping between localized spots). spontaneous grain boundaries form inside the material.
These grain boundaries create regions of local polarization meaning certain parts of the material develop an electric dipole moment. Here Displacement of Pb Ions occurs. This shift causes an imbalance in charge distribution, leading to localized electric fields.
GB⊥ have been observed here. It means the crystal tilts in a direction that is perpendicular to the boundary. Twinning boundaries have lower energy( more stable) when the in-phase octahedral tilting axis is rotated perpendicularly rather than twisted.
Low temperature (<100K) transport can be explained by the Mott’s variable range hopping (VRH) equation. Its conductivity is given by,
P is Local polarization, V is volume, d is displacement of ion
Source: https://arxiv.org/html/2502.20261v1
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