First-principles study of detrimental iodine vacancy in lead halide perovskite under strain and electron injection

Abstract

Vacancy defects are universally regarded to be the main defect that limits the photoelectric conversion efficiency of perovskite solar cells. In perovskite, iodine vacancy dominates the defect proportion due to its low formation energy. However, the defect property of iodine vacancy (VI) is still in dispute. Ideally, the VI defect is considered to be a shallow level defect near conduction band minimum, meaning that it does not act as a Shockley–Read–Hall (SRH) nonradiative recombination center. Herein, we find a direct correlation between compressive strain and VI defect behavior. The compressive strain along the lattice vector b/c direction will drive the VI defect from shallow level to deep level defect, which is related to the formation of Pb-dimer. In addition, the influence of extra electrons is also considered during the structural evolution of VI, which is often observed in the experiments. Therefore, we find that the elimination of compressive strain and extra electrons can be of great significance for improving the photoelectric performance of perovskite solar cells. Our work reveals the defect properties of VI from shallow level one to the SRH recombination center and the inherent physics mechanism of defect evolution under external factors, which provides a strategy to control device defects and eliminate recombination losses.

Highly Efficient Hybrid Perovskite/Organic Tandem White Light Emitting‐Diodes with External Quantum Efficiency Exceeding 20%

“…[27,32,33] Furthermore, the chemical interactions between PPT and perovskites were investigated by electronic structure calculations based on density functional theory (DFT). [34] As shown in Figure 2e, the Pb-Pb dimer defects at the perovskite surface are the domain trap centers, [35] and the introduction of PPT can effectively passivate the surface defects by forming the P═O:Pb bond (Figure 2f). As summarized in Table S2, Supporting Information, the adsorption energy difference (△E ad ) between these two surfaces is calculated to be −0.346 eV, which further confirms the preferred interaction of the P═O group with perovskite defects.…”

Microstress for metal halide perovskite solar cells: from source to influence and management

“…75 (h) The red and blue colors indicate the variation of the standard deviation and the average value of the bond length under different strains in the b and c directions around the V I defect, respectively. 76 gradually decreases from −4% to 4%. When the tensile strain is applied, the length of the Pb-I bond becomes longer, the interaction between them becomes weaker, and I − migrates more easily.…”

“…Moreover, iodine vacancies occupy a large proportion of defects due to their low formation energy in the perovskite crystalline structure. Liu et al 76 discovered that there is a direct relationship between compressive strain and VI defect behavior. In an ideal state, iodine defect is deemed to be a shallow-level defect close to the minimum value of the conduction band, but under compressive strain, it will promote the conversion of iodine defect from shallow to deep energy level, which is related to the formation of Pb dimer.…”

“…(g) Relative DFE of intrinsic defects produced by CsPbI 3 , FAPbI 3 and MAPbI 3 perovskites under different strains 75. (h) The red and blue colors indicate the variation of the standard deviation and the average value of the bond length under different strains in the b and c directions around the V I defect, respectively 76.…”

Beneficial effects of tensile strain on charge carrier lifetime in metal halide perovskites containing halogen vacancies

“…This initiates a number of experimental and theoretical works on the roles of strain in PSCs. [41][42][43][44][45][46][47][48][49] Recent experiments have identified the presence of significant tensile strain in hybrid perovskites, which can be achieved by adopting strategies such as mixing large A-site cations 50 and light illumination. 51 Although the influence of tensile strain on the optoelectronic performance of defect-free hybrid perovskites was investigated, 52 the precise relationship between tensile strain and defect passivation in PSCs has not been fully understood from an atomistic level of theory.…”