Real‐Time In Situ Observation of Microstructural Change in Organometal Halide Perovskite Induced by Thermal Degradation

Abstract

Organometal halide perovskites have demonstrated remarkable achievements in solar cell applications and have attracted tremendous attention as next‐generation photovoltaic materials. Regardless of the unprecedented success, the degradation of the perovskite has caused the performance of the perovskite solar cells to be unreliable and prevented their commercialization. However, the detailed degradation mechanism of the perovskite has yet to be elucidated. In this study, the entire procedure of the thermally induced degradation of methylammonium lead iodide (MAPbI3) is reported using real‐time in situ transmission electron microscopy. The in situ investigation directly illustrates the detailed process of precipitating trigonal PbI2 grains during thermal degradation and confirms that trigonal PbI2 is precipitated from the amorphized MAPbI3 layer via intermediate states. The intermediate states and their stackings enable the generation of 3D linear‐empty spaces that can be utilized as passages by elements during the decomposition and intercalation of the perovskite. This report will provide critical clues for the commercialization of the perovskite‐based solar cells and for further investigation of the synthesis of the perovskite, which is not fully understood.

Transmission electron microscopy of organic-inorganic hybrid perovskites: myths and truths

“…The situation for in situ TEM studies on OIHPs is even worse since under common high resolution TEM (HRTEM) (dose rate: thousands of e Å À2 s À1 ) or high-angle annular dark field scanning TEM (STEM) (dose rate: hundreds or thousands of e Å À2 s À1 ) imaging modes, the total doses within several seconds are large enough to induce damage or full decomposition, likely leading to inaccurate or even incorrect conclusions (see Table S1 online for detailed discussion). For example, Segawa group [17] used in situ HRTEM patterns to record the microstructural changes of MAPbI 3 for 5 min. At such a high dose, the sample is likely PbI 2 rather than MAPbI 3 thus the observed structural changes are likely mainly due to the electron beam irradiation instead of temperature effect.…”

Substance and shadow of formamidinium lead triiodide based solar cells

“…Such information will establish the corelationship between the nanostructure and the physical properties, essential for advancing the design of new materials and interfaces. Research groups are studying techniques such as in-situ grazing-incidence small-angle neutron scattering (GISANS) to gain information about the water uptake [97] , grazing-incidence wide-angle X-ray scattering (GIWAXS) to track moisture-and thermal-induced structural changes [98][99][100][101] , timeof-flight secondary-ion mass spectrometry (ToF-SIMS) to measure the ion distribution and migration during the decomposition [102][103][104] , in-situ high resolution X-ray photoelectron spectroscopy (HR-XPS) to analyse thermal degradation induced compositional changes at the surface [104] , in-situ point-resolved valence electron energy loss spectroscopy (VEELS) to understand the chemistry of the perovskite during thermal degradation [105] and in-situ high resolution transmission electron microscopy (HR-TEM) [106] coupled with their fast Fourier transforms (FFTs) [107] , selected area electron diffraction (SAED) [108] and energy dispersive X-ray analysis (EDX) [109] to visualize the microstructural variations during thermal-, moisture-and electric stress-induced degradation of different perovskites and complete devices. In this direction, FAPbI3 requires a more detailed study in order to grab the real information on composition-microstructure-property-…”

Advanced Characterization Techniques for Overcoming Challenges of Perovskite Solar Cell Materials

“…By comparing quenching rates by in situ heating during HAADF measurements to control perovskite composition and morphology, they provided new insights of correlations between morphology (perovskite coverage and scaffold infiltration), chemical composition (Cl-containing or not), and thermal stability of perovskite materials. In the meantime, several different in situ TEM analyses for thermal degradation of perovskite materials were reported [129][130][131] as shown in Figure 8b,c, respectively. Such in situ TEM heating studies on perovskite materials demonstrated that in-depth understanding of thermal degradation routes and microstructural changes during the degradation can be achieved.…”

“…b) HRTEM images and corresponding FFTs for MAPbI 3 obtained from the in situ TEM under temperature increase from 70 to 150 °C. Reproduced with permission [130]. Copyright 2018, Wiley.…”