*2.2.5. Point defects*

The p‐ or n‐type absorbers were made from materials with intrinsic defects, or using inten‐ tional doping intrinsic defects that create deep energy levels in the absorber usually act as Shockley‐Read‐Hall nonradiative recombination centers and carrier traps, reducing the carrier lifetime and thus *V*oc. A good solar cell absorber must exhibit proper doping and defect prop‐ erties. There are many types of defects as a donor and acceptor which lies in the semiconduc‐ tors. The formation energy of a defect depends on the chemical potential and environmental factors such as precursors, partial pressure, and temperature. So we can conclude that these experimental conditions play a vital role to determine the formation energies of all the pos‐ sible defects and further impact the polar conductivity in these materials. Defect formation energies determine the polar conductivity of a semiconductor, whereas defect transition lev‐ els determine the electrical effect of any particular defect [101].

Besides point defects, Kim et al. [102] used DFT‐GGA to calculate the DOS and partial charge densities of two types of neutral defects in β phase CH3 NH3 PbI3 : (a) Schottky defects (equal numbers of positive and negative vacancies) and (b) Frenkel defects (equal numbers of vacancies and interstitials of the same ion). The tunable polar conductivity and shallow defect properties may help to explain why high‐performance perovskite solar cells, with extremely long carrier lifetimes [40, 103] can be produced by a diverse range of growth approaches and a wide variety of solar cell architectures. These point defects would suggest new methods for perovskite solar cell architecture. It was observed that deep point defect levels could exist through large atomic relaxations, which is attributed to the strong cova‐ lency of the system [104].
