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Density Functional Theory Calculations of Oxygen-Vacancy Formation and Subsequent Molecular Adsorption on Oxide Surfaces
摘要： The surface oxygen vacancy formation energy (EOvac) is an important parameter in determining the catalytic activity of metal oxides. Estimating these energies can therefore lead to data-driven design of promising catalyst candidates. In the present study, we determine EOvac for various insulating and semiconducting oxides. Statistical investigations indicate that the band gap, bulk formation energy, and electron affinity are factors that strongly influence EOvac. Electrons enter defect states after O desorption, and these states can be in the valence band, mid-gap, or in the conduction band. Subsequent adsorption of O2, NO, CO, CO2, and H2 molecules on an O-deficient surface is also investigated. These molecules become preferentially adsorbed at the defect sites, and EOvac is identified as the dominant factor that determines the adsorption mode as well as a descriptor that shows good correlation with the adsorption energy.
关键词： catalytic activity,molecular adsorption,oxygen vacancy formation energy,metal oxides,density functional theory
更新于2025-09-23 15:21:21
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Understanding Molecular Adsorption on CuSCN Surfaces Toward Perovskite Solar Cell Applications
摘要： CuSCN has been employed as the hole transporting material for solar cells and it is established to offer superior power conversion efficiencies and stabilities of the perovskite solar cell. In this manuscript, we carry out first principles calculations to understand the structures and properties CuSCN surfaces in the presence of small molecules that are common in the solution processable solar cells. The molecular adsorbates include additives, precursors and solvents to synthesize the halide perovskite solar cell components such as methylammonium iodide (MAI), lead iodide (PbI2), acetonitrile, chloroform, dimethylformamide (DMF), dimethylsulfoxide (DMSO), methanol and ethanol. The study suggests that the CuSCN surfaces interact with these additive molecules in various degrees and such adsorption is strongly dependent on the CuSCN surface directions. The presence of the PbI2 moiety leads to additional empty states inside the band gap of CuSCN. The presence of the molecular adsorbates impacts on the electronic and optical properties of the CuSCN surfaces, and further additive-based interfacial engineering approach of the perovskite/CuSCN system is called for. This study paves the way toward the fundamental understanding of the CuSCN surfaces toward optoelectronic applications.
关键词： perovskite solar cells,optoelectronic applications,CuSCN,molecular adsorption,first principles calculations
更新于2025-09-19 17:13:59
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Molecular adsorption and strain-induced ferromagnetic semiconductor-metal transition in half-hydrogenated germanene
摘要： Very recently, half-hydrogenated germanene has been achieved in an experiment. In this paper, we investigate the effects of tetracyanoquinodimethane (TCNQ) molecular adsorption and strain on the electronic properties of half-hydrogenated germanene through first-principles. As an electron-acceptor molecule, TCNQ is exploited to non-covalently functionalize the half-hydrogenated germanene. However, this physical adsorption induces a ferromagnetic semiconductor–metal transition in half-hydrogenated germanene due to charge transfer from the substrate to the TCNQ molecule. More importantly, the superstructure of half-hydrogenated germanene/TCNQ is extremely sensitive to biaxial tensile strain. Under the biaxial tensile strain of 0.25%, the ferromagnetic semiconductor–metal transition induced by molecular adsorption can surprisingly be overturned. Meanwhile, a strong p-type doping is exhibited. Remarkably, it would return from a ferromagnetic semiconductor to a metal again when the biaxial tensile strain increases to 1.5%. Our analysis based on the structural and electronic properties of half-hydrogenated germanene/TCNQ indicates that such metal–semiconductor–metal transition in half-hydrogenated germanene/TCNQ under biaxial tensile strain may originate from the strong local deformation, resulting in the energy of the valence band maximum decreasing below or increasing above the Fermi level.
关键词： ferromagnetic semiconductor–metal transition,p-type doping,half-hydrogenated germanene,TCNQ molecular adsorption,biaxial tensile strain
更新于2025-09-10 09:29:36