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ACS Appl Mater Interfaces ; 9(45): 39821-39829, 2017 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-29052974


Nickel oxide (NiO) is a widely used material for efficient hole extraction in optoelectronic devices. However, its surface characteristics strongly depend on the processing history and exposure to adsorbates. To achieve controllability of the electronic and chemical properties of solution-processed nickel oxide (sNiO), we functionalize its surface with a self-assembled monolayer (SAM) of 4-cyanophenylphosphonic acid. A detailed analysis of infrared and photoelectron spectroscopy shows the chemisorption of the molecules with a nominal layer thickness of around one monolayer and gives an insight into the chemical composition of the SAM. Density functional theory calculations reveal the possible binding configurations. By the application of the SAM, we increase the sNiO work function by up to 0.8 eV. When incorporated in organic solar cells, the increase in work function and improved energy level alignment to the donor does not lead to a higher fill factor of these cells. Instead, we observe the formation of a transport barrier, which can be reduced by increasing the conductivity of the sNiO through doping with copper oxide. We conclude that the widespread assumption of maximizing the fill factor by only matching the work function of the oxide charge extraction layer with the energy levels in the active material is a too narrow approach. Successful implementation of interface modifiers is only possible with a sufficiently high charge carrier concentration in the oxide interlayer to support efficient charge transfer across the interface.

Phys Chem Chem Phys ; 18(12): 8723-9, 2016 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-26954607


Based on a comprehensive investigation including ab initio phonon and finite-temperature molecular dynamics calculations, we find that two-dimensional tricycle-shaped arsenene (T-As) is robust and even stable under high temperature. T-As is energetically comparable to previously reported chair-shaped arsenene (C-As) and more stable than stirrup-shaped arsenene (S-As). In contrast to C-As and S-As, the monolayer T-As is a direct band gap semiconductor with an energy gap of 1.377 eV. Our results indicate that the electronic structure of T-As can be effectively modulated by stacking, strain, and patterning, which shows great potential of T-As in future nano-electronics. Moreover, by absorbing H or F atoms on the surface of T-As along a specific direction, nanoribbons with desired edge type and even width can be obtained, which is suitable for the fabrication of nano-devices.

Phys Chem Chem Phys ; 18(2): 1172-7, 2016 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-26660335


Two novel two-dimensional (2D) carbon allotropes named C(y) and C(z) with large meshes are predicted based on first-principles calculations. Their formation energies are lower than that of graphdiyne, which was recently synthesized in an experiment. Molecular dynamics simulations indicate that C(y) and C(z) are stable even when the temperature is over 1000 K. The calculated Poisson's ratios of C(y) and C(z) show their anisotropic mechanical properties. The electronic structure calculations indicate that C(y) is a metal, while C(z) behaves as a semiconductor. Moreover, C(z) shows conductive anisotropy suggesting its potential in nanoelectronic devices. Meanwhile, their well-defined mesh structures are suitable for molecular sieves.

Phys Chem Chem Phys ; 17(47): 32009-15, 2015 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-26573995


Three two-dimensional phosphorus nitride (PN) monolayer sheets (named as α-, ß-, and γ-PN, respectively) with fantastic structures and properties are predicted based on first-principles calculations. The α-PN and γ-PN have a buckled structure, whereas ß-PN shows puckered characteristics. Their unique structures endow these atomic PN sheets with high dynamic stabilities and anisotropic mechanical properties. They are all indirect semiconductors and their band gap sensitively depends on the in-plane strain. Moreover, the nanoribbons patterned from these three PN monolayers demonstrate a remarkable quantum size effect. In particular, the zigzag α-PN nanoribbon shows size-dependent ferromagnetism. Their significant properties show potential in nano-electronics. The synthesis of the three phases of the PN monolayer sheet is proposed theoretically, which is deserving of further study in experiments.