Toward Efficient and Stable Perovskite Solar Cells: Choosing Appropriate Passivator to Specific Defects

Abstract

Figure 3. The impact of MABr treatment on the scanning electron microscopy (SEM) images of film morphology (MAPbI 3 films a) without and b) with MABr treatment), c) ultraviolet-visible (UV-vis) absorption spectra, and d) XRD patterns of the perovskite films. Reproduced with permission. [61] Copyright 2016, Springer Nature. e) Schematic illustration and f) SEM images of the molecule-passivated RP/3D heterostructure. Reproduced with permission. [115] Copyright 2018, Royal Society of Chemistry. g) Schematic representation of the 1D/3D heterostructure evidenced by solid-state NMR proximity measurements. Reproduced with permission. [40] Copyright 2019, Springer Nature. h) Secondary-ion mass spectrometry (SIMS) measurement of interdiffusion-grown MAPbI 3 films on indium tin oxide (ITO) glass. Reproduced with permission.

Defects and Their Passivation in Hybrid Halide Perovskites toward Solar Cell Applications

“…Such shallow defects hence contribute to overall carrier concentrations instead of deep‐level nonradiative intraband trap states. [ 45 ] Generally, radiative band edge defects are expected to form at very high concentrations; although beneficial for light‐emitting diodes (LEDs), it is highly undesirable for solar cell applications. Defect‐tolerant studies in other systems such as transition metal dichalcogenides and other semiconductors, as shown in Figure a,b, indicate that the tendency of a material to form defect states within the bandgap is primarily influenced by the similarity of orbital characters near the conduction and valence bands of semiconductors with antibonding valence band.…”

“…[ 44 ] Furthermore, DFT studies with different halide anions and monovalent cations confirmed that the defect landscape in these hybrid halide perovskites varies with composition; different perovskites have different dominant defects depending on their formation energy and balance among the possible existing defects. [ 45 ]…”

“…The addition of iodine led to the formation of I 3 − , which passivated iodine vacancies. [ 45,85 ] However, the amount of excess iodine has to be optimized to achieve an optimum performance. We would like to mention here that defect passivation through excess iodine can be accomplished by adding both excess CH 3 NH 3 PbI 3 and PbI 2 in the precursor.…”

“…[43] It should be keep in mind that a combination of defects can also create dynamic defect states such as edge location (1D) and grain boundary (GB) defects (2D). [44,45] In Figure 1, we have illustrated all possible point defects in a 3D perovskite lattice (ABX 3 ), where yellow, purple, and blue dots represent the A, B, and X site, respectively, and green dots imply external impurity atoms. [43] A pioneering work in this direction has been conducted by Yin et al to study the formation energy of all intrinsic defects in the bulk of the prototype MAPbI 3 perovskite.…”

“…[44] Furthermore, DFT studies with different halide anions and monovalent cations confirmed that the defect landscape in these hybrid halide perovskites varies with composition; different perovskites have different dominant defects depending on their formation energy and balance among the possible existing defects. [45] In another notable study, DFT with generalized gradient approximation (DFT-GGA) calculations revealed the influence of Frenkel and Schottky defects on MAPbI 3 and inferred that the Schottky defects do not form trap states in the bandgap. [49] Similarly, an interesting study on the defect properties of MAPbI 3 through semilocal exchange correlation functionals, such as density functional theory-Perdew-Burke-Ernzerhof (DFT-PBE) calculations, concluded that most of the point defects in MAPbI 3 form shallow states (except I i which forms deep-level states) and do not affect the electronic properties of the perovskite.…”