Structural and Chemical Changes to CH₃NH₃PbI₃ Induced by Electron and Gallium Ion Beams

Abstract

Organic-inorganic hybrid perovskites, such as CH NH PbI have shown highly promising photovoltaic performance. Electron microscopy (EM) is a powerful tool for studying the crystallography, morphology, interfaces, lattice defects, composition, and charge carrier collection and recombination properties at the nanoscale. Here, the sensitivity of CH NH PbI to electron beam irradiation is examined. CH NH PbI undergoes continuous structural and compositional changes with increasing electron dose, with the total dose, rather than dose rate, being the key operative parameter. Importantly, the first structural change is subtle and easily missed and occurs after an electron dose significantly smaller than that typically applied in conventional EM techniques. The electron dose conditions under which these structural changes occur are identified. With appropriate dose-minimization techniques, electron diffraction patterns can be obtained from pristine material consistent with the tetragonal CH NH PbI phases determined by X-ray diffraction. Radiation damage incurred at liquid nitrogen temperatures and using Ga irradiation in a focused ion beam instrument are also examined. Finally, some simple guidelines for how to minimize electron-beam-induced artifacts when using EM to study hybrid perovskite materials are provided.

Stability of Halide Perovskite Solar Cell Devices: In Situ Observation of Oxygen Diffusion under Biasing

“…Imaging was done with FEI‐Titan TEM with a Oneview CCD detector (Gatan) that allowed rapid acquisition (0.2–0.3 s). Therefore, the total dose was limited to 2–3 e Å −2 in order to prevent irradiation effect as reported previously . Additionally, the sample was not constantly irradiated by the electron beam during the TEM measurements; the beam was turned on only when images were being taken, and it was spread out and turned off when in situ biasing was performed.…”

I2 vapor-induced degradation of formamidinium lead iodide based perovskite solar cells under heat–light soaking conditions

“…The samples were then quickly transferred in the air (o2 min) to an FEI Osiris transmission electron microscope, which was operated at 200 kV with a scanning TEM beam current of 250 pA. Energy dispersive X-ray spectroscopy maps were recorded with a dwell time of 400 ms over 512 Â 512 pixels (corresponding to doses of 5-350 pA nm À2 depending on the resolution of the EDX maps), and quantified using the Cliff-Lorimer method 86 with the Bruker Esprit software. While the FIB sample preparation is known to modify the crystallography of metal halide perovskites on the nanometer scale by creating PbI 2 nanodomains, 9,87 the method is most suited to maintain the overall morphology of the layer stack and does not alter the distribution of elements on the 410 nm scale (except where re-deposition of material occurs due to the presence of pores, indicated by arrows in Fig. 4c).…”

“…3c-e) due to the preferential sputtering of the perovskite regions not in direct contact with the top electrode and hence directly in the line of sight of the gallium ions. The electron doses involved during the acquisition of the STEM EDX maps led to amorphization 88 of the absorber and a slight loss of halides due to knock-on damage, 87 but not an overall change in microstructure. TGA-MS. Thermogravimetric analysis-mass spectrometry (TGA-MS) experiments were conducted on a Netzsch STA449 F3 Jupiter DSC/TG apparatus coupled with a Netzsch QMS 403 mass spectrometer.…”

General Decomposition Pathway of Organic–Inorganic Hybrid Perovskites through an Intermediate Superstructure and its Suppression Mechanism

“…[ 25 ] Additional superstructure reflections emerge with increased beam illumination dose, one of which is indicated by the red circle in Figure 1c that, however, is forbidden in tetragonal MAPbI 3 , as we reported earlier. [ 24 ] While both the octahedral tilt [ 26,27 ] and ordered vacancies [ 28 ] can lead to superstructure diffraction spots in perovskite oxides, for MAPbI 3 we interpret such superstructure as vacancies ordering, since OIHPs are prone to lose negatively charged halide ions under electron beam illumination. [ 29 ] Indeed, the simulated ED patterns (Figure 1d) of the MAPbI 2.5 with ordered iodine vacancies (Figure 1e) exactly match the experimental ED patterns along both [001] C (Figure 1c) and [110] C (Figure S2, Supporting Information) directions (subscript C denotes pseudocubic index), and such superstructure has in fact been reported in a variety of perovskite oxides in the form of ABO 2.5 .…”