Nature | 2021
Perovskite decomposition and missing crystal planes in HRTEM
Abstract
Organic–inorganic hybrid perovskites have recently emerged as a new class of semiconductor for high-performance optoelectronic devices, but their extreme sensitivity to electron beam irradiation hinders our ability to obtain the intrinsic structures from high-resolution transmission electron microscopy (HRTEM) characterizations. Ning and co-workers reported lead sulfide (PbS) quantum dots in methylammonium lead iodide (MAPbI3) solids with perfect lattice matching, on the basis of confirmation from HRTEM, electron diffraction and other studies. However, I have found that some crystal planes were missing in their characterizations, and as demonstrated below, the material in their figures cannot be MAPbI3, but possibly lead iodide (PbI2)—the product of perovskite decomposed by electron-beam irradiation. This finding aims to raise awareness among researchers and avoid possible mistakes in the HRTEM characterization of electron-beam-sensitive materials in the future. It is noteworthy that only the (22̄4), (224) crystal planes appear, and that the (11̄2), (112) crystal planes are missing in HRTEM characterizations in the original paper. Figure 1a shows the structure of MAPbI3 and Fig. 1b shows the simulated electron diffraction along the [2̄01] zone axis. Clearly, (11̄2), (112) planes exist in the electron diffraction pattern. Moreover, (11̄2), (112) planes are also present in HRTEM images under low electron dose, selected-area electron diffraction (SAED) and X-ray diffraction (XRD) characterizations. Figure 1c gives the structure of PbS and Fig. 1d shows the simulated electron diffraction along the [111̄] zone axis. Unlike the I4/mcm space group of tetragonal MAPbI3, the Fm m 3̄ space group of cubic PbS displays systematic extinction, so there should be no {101} planes visible in the electron diffraction pattern of PbS phase. MAPbI3 perovskite is very sensitive to electron-beam irradiation and begins to decompose into PbI2 under 151 e Å −2 total dose irradiation (e, electron charge). The absence of crystal planes indicates that the material is no longer MAPbI3 perovskite, but other phases and structures. Figure 1e shows the structure of PbI2 and Fig. 1f shows the electron diffraction pattern along the [88̄1] axis zone, which is consistent with the parameters in the original paper. Importantly, the angle between (22̄4) and (224) is about 57°, not 60° under exact measurement in the https://doi.org/10.1038/s41586-021-03423-4