Transformation and degradation of metal halide perovskites induced by energetic electrons and their practical implications

Abstract

Transmission electron microscopy (TEM) has been used in the characterizations of the lattice and defect structures as well as electronic and chemical properties of various materials. When TEM analyses were performed on lead halide perovskites (LHPs) and related materials, it has often been found that transformation and damage were easily induced in the specimens by electron beam irradiation. As the structural and chemical instabilities of LHPs and related materials are the main obstacle that must be overcome for their practical large-scale applications in solar cells and other optoelectronic applications, we examine whether and how the TEM-based irradiation and analyses can serve the purpose of rapid evaluation of the instabilities of a LHP to stimuli such as light and electric field which are crucial to its optoelectronic applications. We first provide a brief overview of the basic physical properties of LHPs related to the instability and the current understanding of the general mechanisms of sample damages induced by energetic electrons, followed with an analysis of the distinctive vulnerability and damaging features of LHPs with respect to electron beam irradiation. Based on the analysis of the similarities in the mechanisms of the damages generated by different stimuli, proper conditions are outlined with which the TEM-based investigations can be employed as a speed-up tester for the instabilities of LHPs against photon (including visible, ultraviolet and x-ray) exposure and an applied electric field. Furthermore, the perspectives of employing TEM-based processes in the fabrication of nanostructures and directly carrying out subsequent in situ analysis are elaborated, which is key to acquiring knowledge for improving focused electron beam-based industrial micro- and nanofabrication technologies.

Phase Segregation Mechanisms in Mixed-Halide CsPb(BrxI1–x)3 Nanocrystals in Dependence of Their Sizes and Their Initial [Br]:[I] Ratios

“…Step 1: The incoming electromagnetic field (electron beam or light) excites an electron from the valence-band to the conduction-band . The valence-band maximum consists of a halide orbital .…”

“…Generally, an electron beam can cause (a) atomic displacement (knock-on damage), (b) radiolysis (ionization of material), i.e., losses between a few eV for excitation of conduction or valence electrons and tens or hundreds of eV for ionization of inner atomic shells, (c) creation of excitons (band transitions in the material), and (d) generation of phonons/heating in the investigated material. Detailed theory of the different interaction processes and their scattering cross-sections can be found in publications by Egerton et al − Dang et al investigated experimentally the electron-beam damage in LHPs in detail − and applied Egerton’s interaction theory to halide perovskites . From Dang’s work and also from the work by other authors, − it has been established that radiolysis is the main damage process for electron irradiation in LHP.…”

Characterization Tools to Probe Degradation Mechanisms in Organic and Perovskite Solar Cells

“…[93] In situ EM techniques primarily include SEM and TEM, regarded as one of the best tools for studying microstructures of materials due to their high resolution and 3D image capabilities. [235] Using in situ EM, it is possible to dynamically and precisely monitor changes in the surface morphology and microstructure of OSCs and PSCs as they degrade under various stressors. [236] Multiple reactions are triggered in OSCs and PSCs due to external stimuli, eventually resulting in degradation.…”

A Review on Halide Perovskite-Based Photocatalysts: Key Factors and Challenges

“…Dang et al were able to demonstrate the decomposition of CsPbBr 3 nanosheets and nucleation into CsBr, CsPb, and PbBr 2 crystalline domains . Several research papers have tackled the challenges related to TEM analysis of HPs in more detail. − …”

“… 184 Several research papers have tackled the challenges related to TEM analysis of HPs in more detail. 185 − 188 …”