Correlation between Interfacial Structures and Device Performance: The Double-Edged Sword Effect of Lead Iodide in Perovskite Solar Cells.

The interfacial electronic structure of perovskite layers and transport layers is critical for the performance and stability of perovskite solar cells (PSCs). The device performance of PSCs can generally be improved by adding a slight excess of lead iodide (PbI2 ) to the precursor solution. However, its underlying working mechanism is controversial. Here, we performed a comprehensive study of the electronic structures at the interface between CH3 NH3 PbI3 and C60 with and without the modification of PbI2 using in situ photoemission spectroscopy measurements. The correlation between the interfacial structures and the device performance was explored based on performance and stability tests. We found that there is an interfacial dipole reversal, and the downward band bending is larger at the CH3 NH3 PbI3 /C60 interface with the modification of PbI2 as compared to that without PbI2 . Therefore, PSCs with PbI2 modification exhibit faster charge carrier transport and slower carrier recombination. Nevertheless, the modification of PbI2 undermines the device stability due to aggravated iodide migration. Our findings provide a fundamental understanding of the CH3 NH3 PbI3 /C60 interfacial structure from the perspective of the atomic layer and insight into the double-edged sword effect of PbI2 as an additive.

Modulating Nanoparticle Structure by Metal-Metal Oxide Interfacial Interaction in a CeO2-Supported Bimetallic System: The Ni-Cu Case.

Structure-optimized bimetallic and multicomponent catalysts often outperform single-component catalysts, inspiring a detailed investigation of metal-metal and metal-support interactions in the system. We investigated the geometric and electronic structures of ceria-supported Ni-Cu particles prepared using different metal deposition sequences employing a combination of X-ray photoelectron spectroscopy, resonant photoemission spectroscopy, and infrared reflection absorption spectroscopy. The bimetallic model catalyst structure was altered by a distinct surface evolution process determined by the metal deposition sequence. The postdeposited Cu stays on the surface of Ni predeposited CeO2 and forms only a limited Ni-Cu alloy in the Cu-contacted Ni region. However, when Ni is deposited on the Cu predeposited CeO2 surface, Ni can migrate through the Cu layer to the Cu-ceria interface and form an extended Ni-Cu alloy to the whole deposited metal layer on the ceria surface. The dynamic metal diffusion in the CeO2-supported Ni-Cu system indicates that metal-support interactions can be used to achieve the rational design of a bimetallic composition distribution during catalyst preparation.