Using first-principles calculations, we show that p-doped blue phosphorene can be obtained by molecular doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6-TNAP), whereas n-doped blue phosphorene can be realized by doping with tetrathiafulvalene (TTF) and cyclooctadecanonaene (CCO). Moreover, the doping gap can be effectively modulated in each case by applying an external perpendicular electric field. The optical absorption of blue phosphorene can be considerably enhanced in a broad spectral range through the adsorption of CCO, F4-TCNQ, and F6-TNAP molecules, suggesting potential of the doped materials in the field of renewable energy.

Molar fractions are used in applied diffusion kinetics for incorporating thermodynamic and kinetic databases. Molar quantities (molar concentration and molar flux) and reduced molar quantities (molar fraction and reduced molar flux) usually are regarded to be equivalent; i.e., molar quantities are replaced with their reduced forms. However, as the fluxes are related to material properties, the diffusion equations expressed in molar fractions are not consistent with the normalization condition of molar fractions. We develop diffusion kinetics consistent with this condition. Our method is applicable to diffusion with total reduced flux, such as diffusion in an external field or flow field. As two case studies, the developed method is used to investigate ionic diffusion in an electrolyte solution and ionic demixing in a semiconductor oxide.

The application of liquid-exfoliated 2D transition metal disulfides (TMDs) as the hole transport layers (HTLs) in nonfullerene-based organic solar cells is reported. It is shown that solution processing of few-layer WS2 or MoS2 suspensions directly onto transparent indium tin oxide (ITO) electrodes changes their work function without the need for any further treatment. HTLs comprising WS2 are found to exhibit higher uniformity on ITO than those of MoS2 and consistently yield solar cells with superior power conversion efficiency (PCE), improved fill factor (FF), enhanced short-circuit current (JSC), and lower series resistance than devices based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and MoS2. Cells based on the ternary bulk-heterojunction PBDB-T-2F:Y6:PC71BM with WS2 as the HTL exhibit the highest PCE of 17%, with an FF of 78%, open-circuit voltage of 0.84 V, and a JSC of 26 mA cm−2. Analysis of the cells' optical and carrier recombination characteristics indicates that the enhanced performance is most likely attributed to a combination of favorable photonic structure and reduced bimolecular recombination losses in WS2-based cells. The achieved PCE is the highest reported to date for organic solar cells comprised of 2D charge transport interlayers and highlights the potential of TMDs as inexpensive HTLs for high-efficiency organic photovoltaics.

Using first-principles calculations, we investigate selected defects in blue phosphorene (BlueP). For a single-vacancy (SV) defect, a 5-9 structure is energetically favorable, and for a double-vacancy defect, a 5-8-5 or 555-777 structure is. A P adatom favors the top adsorption site. Scanning tunneling microscopy images are simulated to aid the experimental identification of the defects. Formation of a Stone-Wales defect is found to be most likely, but it can be reverted by thermal annealing. Calculated migration and transformation barriers show that a SV defect can migrate easily. Both a SV defect and a P adatom induce a magnetic moment, thus turning BlueP into a magnetic semiconductor. It turns out that all of the defects under investigation enhance the ability of BlueP to absorb sunlight.

First-principles calculations are performed to compare the adsorption of CO, NH3, NO, and NO2 molecules on monolayer, bilayer, and heterobilayer MoS2 and WS2, using van der Waals corrected density functional theory. Only minor differences are demonstrated for the adsorption behaviors of the monolayer and bilayer systems despite fundamental differences in the electronic structure (direct versus indirect band gap). We also show that NO2 binds stronger to the sensor materials than the other gas molecules, resulting in enhanced charge transfer. Adsorption of paramagnetic NO and NO2 has significant impact on the electronic states, in contrast to adsorption of nonmagnetic CO and NH3.

The confined variational method is applied to investigate the low-energy elastic scattering of orthopositronium from H2 by first-principles quantum mechanics. Describing the correlations with explicitly correlated Gaussians, we obtain accurate s-wave phase shifts and pickoff annihilation parameters for different incident momenta. By a least-squares fit of the data to the effective-range theory, we determine the s-wave scattering length AS=2.02a0 and the zero-energy value of the pickoff annihilation parameter, 1Zeff=0.1839. The obtained 1Zeff agrees well with the precise experimental value of 0.186(1) [G. L. Wright, J. Phys. B 16, 4065 (1983)10.1088/0022-3700/16/21/027] and the obtained AS agrees well with the value of 2.1(2)a0 estimated from the average experimental momentum-transfer cross section for positronium energy below 0.3 eV [F. Saito, J. Phys. B 36, 4191 (2003)10.1088/0953-4075/36/20/011].

Copper thiocyanate (CuSCN) and copper selenocyanate (CuSeCN) combine a high work function with a high optical transparency. To elucidate their potential as transparent hole selective materials, herein, first-principles calculations of the structural and electronic properties are reported, with special attention to the band offsets with crystalline Si and hybrid perovskites (CH3NH3PbI3, CH3NH3PbBr3, and CHN2H4PbBr3). The structural parameters and electronic band structure are obtained using the Perdew–Burke–Ernzerhof functional, resulting in indirect and direct bandgaps of 2.13 and 1.81 eV for CuSCN and CuSeCN, respectively. The (100) surfaces of the two materials do not feature in-gap states, maintaining the semiconducting nature. Band offsets are determined by the electrostatic potential lineup method using slab calculations. Small valence band offsets of 0.10 eV for CuSCN/Si and 0.08 eV for CuSCN/CH3NH3PbI3 are desirably found, i.e., a promising hole transport layer character of CuSCN for Si and CH3NH3PbI3-based solar cells. Type-II band alignment is obtained for all studied heterojunctions.

Dehumidification is a critical energy-intensive and crucial process for several industries (e.g., air conditioning and gas dehydration). Polymeric membranes with high water vapor permeability and selectivity are needed to achieve an energy-efficient water vapor removal. Herein, we demonstrate high-performance water vapor transport membranes based on novel amphiphilic tercopolymers. A series of amphiphilic tercopolymers comprising polyacrylonitrile, poly(ethylene glycol) methyl ether methacrylate (PEGMA), and poly(N,N-dimethylamino ethyl methacrylate) (PDMAEMA) segments are synthesized via an economical and facile free radical polymerization. The water vapor permeability increases with the increase in PEGMA chain length and the content of PEGMA segments. The best performing membrane (i.e., PEGMA-9502) achieved a water vapor permeability of 174 kBarrer. By optimizing the content and chain length of the PEGMA segments, the membranes could be tuned for carbon capture applications. The optimized membranes tested for CO2 separation showed a high CO2 permeability of 47 Barrer along with CO2/N2 and CO2/CH4 selectivities of 67 and 23, respectively. This work presents a simple and economic amphiphilic tercopolymer for the fabrication of membranes with excellent gas and water vapor separation performance.

Adsorption of S-containing gases on pristine, defective, and heteroatom doped stanene is studied for gas sensing applications by van der Waals corrected density functional theory. SO2 and H2S gas molecules are found to bind to pristine stanene too weakly to alter the electronic properties sufficiently for efficient gas sensing (binding energy of −0.20 and −0.33 eV, respectively). We demonstrate that vacancies and heteroatom doping can enhance the binding energy to −1.67 and −0.74 eV, respectively. It is found that presence of mono-vacancies, tri-vacancies, and In dopants at low concentrations in stanene results in considerable variations of the electronic properties in contact with S-containing gases, thus transforming stanene into an efficient sensing material.

A multi-scale approach is employed to design metal-organic frameworks (MOFs). The methane sorption properties are studied by grand canonical Monte Carlo simulations to reveal the structure-property relationship with respect to the methane total uptake and working capacity at different temperatures and pressures. We identify rhr-MOFs with outstanding gravimetric working capacity. For example, the BBB MOF (largest studied pore size) achieves a value of 60.7 wt% at 298 K and 5–65 bar.