Abstract
Understanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and understand failure mechanism. Here, using low-dose imaging technique by direct-detection electron-counting camera in a transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH3NH3PbI3 (MAPbI3) at the atomic scale. We successfully image the atomic structure of perovskite in real space under ultra-low electron dose condition, and observe a two-step decomposition process, i.e., initial loss of MA+ followed by the collapse of perovskite structure into 6H-PbI2 with their critical threshold doses also determined. Interestingly, an intermediate phase (MA0.5PbI3) with locally ordered vacancies can robustly exist before perovskite collapses, enlightening strategies for prevention and recovery of perovskite structure during the degradation. Associated with the structure evolution, the bandgap gradually increases from ~1.6 eV to ~2.1 eV. In addition, it is found that C-N bonds can be readily destroyed under irradiation, releasing NH3 and HI and leaving hydrocarbons. These findings enhance our understanding of the photoelectric properties and failure mechanism of MAPbI3, providing potential strategies into material optimization.
Highlights
Understanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and understand failure mechanism
While much progress has been made in transmission electron microscopy (TEM) characterizations of Organic-inorganic hybrid perovskites (OIHPs), direct visualization of atomic structure remains to be elusive
It is noted that sufficient dose (Supplementary Fig. 2) is needed to obtain images with good quality and superstructure diffraction reflections appear due to the generation of intermediate phases when the dose is larger than 2.7 e Å−2 (Fig. 1b, g)
Summary
Understanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and understand failure mechanism. Using low-dose imaging technique by direct-detection electroncounting camera in a transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH3NH3PbI3 (MAPbI3) at the atomic scale. The organic cations as well as the hydrogen bonding may lead to spontaneous polarization and ferroelectricity[11], which promotes the separation of photoexcited electron-hole pairs, and reduces the recombination and improves the carrier lifetime[12] These characteristics are responsible for the promising optoelectronic properties including high carrier mobility, long charge diffusion length and superior power conversion efficiency[13]. The damage-free pristine structure of MAPbI3 has not been imaged at the atomic scale, and the corresponding real-space degradation pathway is yet to be established, motivating this study
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