Interfacial properties
of perovskite layers and metal electrodes play a crucial role in device
performance and long-term stability of perovskite solar cells. In
this work, we performed a comprehensive study of the interfacial structures
and ion migration at the interface of a CH3NH3PbI3 perovskite layer and an Al electrode using in situ
synchrotron radiation photoemission spectroscopy measurements. It
was found that the Al electrode can react with the perovskite layers,
leading to the formation of aluminum iodide species and the bonding
between Al and N, as well as the reduction of Pb2+ ions
to metallic Pb species at the interface. Moreover, during the Al deposition,
iodide ions can migrate from the CH3NH3PbI3 subsurface to the Al electrode, while the reduced Pb remains
at the subsurface. The depth profile photoemission measurements, made
by varying the photon energies of incident synchrotron radiation X-rays,
demonstrate that the reaction occurs at the Al/CH3NH3PbI3 interface at least with a thickness of ∼3.5
nm below the perovskite surface. This study provides an atomic-level
fundamental understanding of the Al/CH3NH3PbI3 interfacial structures and insight into the degradation mechanisms
of perovskite solar cells when using Al metal as the electrode.
Atomic intercalation can be utilized to engineer the electronic structure of two dimensional layered materials at the atomic scale, thereby governing distinctive properties in comparison with the pristine ones. Herein, a minute amount of Rhenium (Re) atoms (∼1.3% wt.) were controllably intercalated inside the layers of semiconducting Zirconium diselenide (ZrSe2) single crystal. Our angle-resolved photoemission spectroscopy revealed that Re intercalation could move down the bottom of the ZrSe2 conduction band without band dispersion changes, resulting in a small electronic pocket at the Brillouin zone boundary at the M point. The subsequent low-temperature transport results further confirmed the anomalous metallic characteristics in the semiconducting ZrSe2 after low-level Re intercalation.
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