*2.2.6. Structural disorder*

In a recent investigation, Choi et al. [105] found that most of CH3 NH3 PbI3 (70%) is highly disordered with a local perovskite structure extending over a range of only 1.4 nm, which is about 2 lattice constants of the α phase [106].

The mesoporous scaffold confined need the perovskite within the pores and reshaped the structures of perovskites. On the other hand, the low‐temperature growth process inevita‐ bly leads to polycrystalline perovskites with grain boundaries (GBs). Experimentally, it is very difficult to investigate the structural and electronic properties directly, as it requires a high resolution transmission spectroscopy (HRTEM). So, we have to rely on the theoretical calculations that can give direct insights into the electrical properties of structural disorders and topological defects in hybrid perovskites. Recent combined theoretical and experimental studies [106] have demonstrated that Cl segregated into the GB part of polycrystalline CdTe solar cells effectively taming the detrimental effects at GBs.

Due to the structural complicity of CH3 NH3 PbI3 , the GB structures were constructed based on CsPbI3 . It was observed that the DOS of the supercells with GBs are very similar to those of single‐crystal phases. None of these GBs introduce defect states within the bandgap region. The GW band structure diagram is given in **Figure 8**.

**Figure 8.** DOS graph of MASnI3 and MAPbI3 materials. Adapted with permission from reference [116].
