Impact of iodine antisite (IPb) defects on the electronic properties of the (110) CH3NH3PbI3 surface

Abstract

The power conversion efficiency of perovskite solar cells can be significantly improved if recombination losses and hysteresis effects, often caused by the presence of structural and chemical defects present at grain boundaries and interfaces, can be minimized during the processing of photoactive layers. As a crucial first step to address this issue, we performed density functional theory calculations to evaluate the electronic structure of the energetically favored (110) perovskite surface in the presence of the widely reported IPb antisite defects. Our calculations indicate that the nature of trap states formed is different for the perovskite surface with exposed methylammonium (MAI) and lead iodide (PbI2) terminating groups. While, in MAI terminated surfaces, IPb antisite defects lead to shallow states close to the valence band, both deep and shallow states are created in the bandgap region in the PbI2 terminated surface. Furthermore, we determined contribution from individual atoms to the trap states and inferred that the trap states originate from the clusters of iodine atoms that are formed near the defect site. The exact nature of the defect state is strongly correlated with the atomic structure of these clusters and can be potentially tuned by controlling the processing conditions of the perovskite film.

Origin, Influence, and Countermeasures of Defects in Perovskite Solar Cells

“…Conversely, defects on the perovskite surface can potentially alter the local atomic arrangement of the surface and conclusively affect its nature. [99] PbI anti-site defect (i.e., Pb I and I Pb ) is the most anticipated deep trap in perovskite because the presence of anti-site defects introduces covalent bonds, resulting in the formation of new bonds between the defect atoms and other chemicals, thereby forming electron trap states in the bandgap region. [99] It has been shown that the formation of Pb I defect on the surface can Reproduced with permission.…”

“…[99] PbI anti-site defect (i.e., Pb I and I Pb ) is the most anticipated deep trap in perovskite because the presence of anti-site defects introduces covalent bonds, resulting in the formation of new bonds between the defect atoms and other chemicals, thereby forming electron trap states in the bandgap region. [99] It has been shown that the formation of Pb I defect on the surface can Reproduced with permission. [87] Copyright 2017, American Chemical Society Publications.…”

Realizing Reduced Imperfections via Quantum Dots Interdiffusion in High Efficiency Perovskite Solar Cells

“…It is reported that the nature of the defect state is strongly correlated with the atomic structure of the cluster‐terminated surface. [ 34,67 ] The potential shallow defect generated from the Pb I antisite is the domination of ionic defects on the surface, which is could primarily be responsible for the loss in V oc . [ 36,68 ] Therefore, it is suggested that the treatment of OIHP film with QDs‐Cs5 is able to effectively suppress Pb I antistite defects at the surface via QDs solid‐state interdiffusion.…”

Unraveling the Photogenerated Electron Localization on the Defect-Free CH3NH3PbI3(001) Surfaces: Understanding and Implications from a First-Principles Study

“…Uratani et al reported evidence of the presence of surface defects leading to trapping electrons 36 . The halide vacancy is one of the most common defects and several studies revealed that the iodine and bromine vacancies resulted in the formation of charge trapping [37][38][39][40][41] .…”