Designing Organic Electron Transport Materials for Stable and Efficient Performance of Perovskite Solar Cells: A Theoretical Study.

In this article, electron transporting layer (ETL) materials are designed to enhance the performance and stability of methyl ammonium lead iodide (MAPbI3) perovskite solar cells (PSCs). The optical and electronic properties of the designed ETLs are investigated using density functional theory. The designed ETLs show better charge mobility compared to nickel phthalocyanines (NiPcs). The NiPc, a hole transporting layer material, shows ETL-like behavior for PSCs with the substitution of different electron withdrawing groups (X = F, Cl, Br, and I). The stability and electron injection behavior of the designed ETLs are improved. The Br16NiPc shows the highest charge mobility. Further, the stability of the designed ETLs is relatively better compared to NiPc. Due to the hydrophobic nature, the designed ETLs act as a passivation layer for perovskites and prevent the absorber materials from degradation in the presence of moisture and provide extra stability to the PSCs. The effect of designed ETLs on the performance of MAPbI3 solar cells is also investigated. The PSCs designed with Br16NiPc as an ETL shows a relatively better (23.23%) power conversion efficiency (PCE) compared to a TiO2-based device (21.55%).

Designing vertically aligned porous NiCo2O4@MnMoO4 Core@Shell nanostructures for high-performance asymmetric supercapacitors.

NiCo2O4@MnMoO4 core@shell nanostructures are synthesized as electrode material using hydrothermal method for the fabrication of asymmetric supercapacitor (ASC) device. The NiCo2O4@MnMoO4 electrode shows better electrochemical performance with specific capacitance (SC) of 1821 F/g at current density of 5 A/g and cycling stability of 94%. The NiCo2O4@MnMoO4 core@shell electrode shows better SC compared to pure NiCo2O4 and MnMoO4 electrodes. An ASC device is fabricated using NiCo2O4@MnMoO4 as a positive and rGO/Fe2O3 as negative electrode materials. Remarkably, the fabricated device shows a SC of 294 F/g at current density 4 A/g, with an energy density of 91.87 Wh/kg at a power density of 374.15 W/kg. The device shows good reversibility with cycling stability of 68% after 2,000 cycles. The ASC device is used to illuminate nine green color LEDs for 35 min. Therefore, the present report provides a simple method to fabricate efficient and stable energy storage devices for industrial applications.

Electronic structure of iron dinitrogen complex [(TPB)FeN2]2-/1-/0: correlation to Mössbauer parameters.

Low-valent species of iron are key intermediates in many important biological processes such as the nitrogenase enzymatic catalytic reaction. These species play a major role in activating highly stable N2 molecules. Thus, there is a clear need to establish the factors which are responsible for the reactivity of the metal-dinitrogen moiety. In this regard, we have investigated the electronic structure of low-valent iron (2-/1-/0) in a [(TPB)FeN2]2-/1-/0 complex using density functional theory (DFT). The variation in the oxidation states of iron in the nitrogenase enzyme cycle is associated with the flexibility of Fe→B bonding. Therefore, the flexibility of Fe→B bonding acts as an electron source that sustains the formation of various oxidation states, which is necessary for the key species in dinitrogen activation. AIM calculations are also performed to understand the strength of Fe→B and Fe-N2 bonds. A detailed interpretation of the contributions to the isomer shift (IS) and quadrupole splitting (ΔE Q) are discussed. The major contribution to IS comes mainly from the 3s-contribution, which differs depending on the d orbital population due to different shielding. The valence shell contribution also comes from the 4s-orbital. The Fe-N2 bond distance has a great influence on the Mössbauer parameters, which are associated with the radial distribution, i.e. the shape of the 4s-orbital and the charge density at the nucleus. A linear relationship between IS with Fe-N2 and ΔE Q with Fe-N2 is observed.

Photodegradation of phenanthrene catalyzed by rGO sheets and disk like structures synthesized using sugar cane juice as a reducing agent.

In the present report, rGO sheets (rG1) and disk (rG2) like structures of reduced graphene oxide (rGO) were synthesized using sugar cane juice as green reducing agent. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis.) spectroscopy and photoluminescence (PL) spectroscopy techniques. The transition of electrons localized in different sized sub-domain of the sp2 bonded carbons having different values of highest occupied molecular orbital (HOMO) -lowest unoccupied molecular orbital (LUMO) gap may likely to be responsible for the observed PL emission in rG1 and rG2 at different excitation wavelengths. The rG1 and rG2 were also used as photocatalyst materials for the degradation of phenanthrene (PHE) under the UV irradiation. The rG2 shows better photocatalytic degradation compared to rG1 by degrading the PHE up to 30%.

Well-controlled in-situ growth of 2D WO3 rectangular sheets on reduced graphene oxide with strong photocatalytic and antibacterial properties.

Finding the materials, which help to control the water pollution caused by organic and bacterial pollutants is one of the challenging tasks for the scientific community. 2D sheets of WO3 and composite of WO3 and reduced graphene oxide (rGO) have been synthesized in a well-controlled way using a hydrothermal method. The as synthesized 2D sheet of WO3 and rGO-WO3 composite were characterized by various techniques. The 2D sheets of WO3 and rGO-WO3 composite are efficiently utilized for the photocatalytic degradation of methylene blue (MB) and Rhodamine B (RhB) dyes under sunlight. The rGO-WO3 composite reveals excellent photocatalytic degradation of RhB dye by degrading it upto 85% under sunlight. However, the MB dye was degraded by 32%. The greater degradation of RhB dye was explained in terms of the molecular electrostatic potential. We found that RhB has a more positive potential compared to MB dye where O2- and OH̊ radicals interact more strongly, resulting in a greater degradation of the RhB dye. The antibacterial activity of the 2D sheets of WO3 and rGO-WO3composite was also investigated on gram positive (B. subtilis) and gram negative (P. aeroginosa) microbes for the first time.

One-pot synthesis of Ni doped CdS nanosheets for near infrared emission and excellent photocatalytic materials for degradation of MB dye under UV and sunlight irradiation.

Undoped CdS nanostructures and Ni (3%, 5% and 7%) doped CdS nanosheets were synthesized via template-free one pot solvothermal method. The synthesized products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy (RS), UV-visible (UV-vis.) spectroscopy, and photoluminescence (PL) spectroscopy techniques. The Ni doped CdS nanosheets excited by 2.75eV revealed two weak near-infrared emission bands at 2.02 and 1.73eV. These two bands may be due to transition from of d electronic state of Ni to hybridized (p-d) state of Ni ions and S. The photodegradation of MB dye with Ni doped nanosheets is more efficient under sunlight compared to UV light irradiation. The 3% Ni doped nanostructures act as an efficient photocatalyst. The presence of Ni2+ generate electron and holes and prolonged the recombination rate by introducing the temporary trapping sites, which essentially causes to improve the photocatalytic efficiency of the synthesized samples.

Investigation of the encapsulation of metal cations (Cu2+, Zn2+, Ca2+ and Ba2+) by the dipeptide Phe-Phe using natural bond orbital theory and molecular dynamics simulation.

Complexes of the dipeptide phenylalanine-phenylalanine (Phe-Phe) with divalent metal cations (Cu2+, Zn2+, Ca2+ and Ba2+) were studied at the B3LYP and MP2 levels of theory with the basis sets 6-311++G(d,p) and 6-31 + G(d) in the gas phase. The relative energies of these complexes indicated that cation-π bidentate/tridentate conformations are more favourable than other conformations with uncoordinated rings. These findings were confirmed by the calculated values of thermodynamic parameters such as the Gibbs free energy. Natural bond orbital (NBO) analysis was carried out to explore the metal-ligand coordination in Phe-Phe-Cu2+/Zn2+ complexes. Possible orbital transitions, types of orbitals and their occupancies were determined for a range of Phe-Phe-Cu2+/Zn2+ complexes. The charge transfer involved in various orbital transitions was explored by considering the second-order perturbation energy. NBO analysis revealed that the change transfer is stronger when the metal cation uses both the 4s + 4p subshells rather than just its 4p subshell. We also performed molecular dynamics (MD) simulations to check the stability and consistency of the most favourable binding motifs of Cu2+, Zn2+, Ca2+ and Ba2+ with Phe-Phe over time. The structures of the Phe-Phe-Cu2+/Zn2+/Ca2+/Ba2+ complexes obtained using MD simulation were found to be in good agreement with those obtained in the DFT-based calculations. Graphical Abstract Conformational search on encapsulation of divalent metal cations (Ca2+, Zn2+, Ca2+, Ba2+) by the Phe-Phe dipeptide.

Facile and controlled synthesis of aligned WO3 nanorods and nanosheets as an efficient photocatalyst material.

In this work, we have performed a facile and controlled synthesis of WO3 nanorods and sheets in different crystal phases (triclinic, orthorhombic and monoclinic) of WO3 using the sol-gel method. The detailed structures of the synthesized materials were examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy measurements. The shapes and crystal phases of the WO3 nanostructures were found to be highly dependent on the calcination temperature. The variation in crystalline phases and shapes is modified the electronic structure of the samples, which causes a variation in the value of optical band gap. The value of the Raman line intensity ratio I264/I320 has been successfully used to identify the structural transition from the triclinic to the orthorhombic phase of WO3. The PL spectra of the synthesized products excited at wavelengths 380, 400, and 420nm exhibit intense emission peaks that cover the complete visible range (blue-green-red). The emission peaks at ~460 and ~486nm were caused by the near band-edge and band to band transition, respectively. The peaks in spectral range 500-600nm might be originated from the presence of oxygen vacancies lying within the energy band gap. The synthesized WO3 nanostructures showed improved photocatalytic activity for the photodegradation of MB dye. The enhanced photocatalytic activity of WO3 nanosheets compared to WO3 nanorods for photodegradation of methylene blue (MB) dye could be due to the shape of the nanostructured WO3. The sheet type of structure provides more active surface for the interaction of dye molecules compared to the rods, which results in a more efficient degradation of the dye molecules.

Cadmium oxide nanoparticles grown in situ on reduced graphene oxide for enhanced photocatalytic degradation of methylene blue dye under ultraviolet irradiation.

Cadmium oxide (CdO) nanoparticles (NPs), reduced graphene oxide (rGO) and rGO-CdO nanocomposites have been synthesized using one step hydrothermal method. The structural and optical properties of CdO NPs, rGO, and rGO-CdO nanocomposites were investigated by X-ray diffraction (XRD), energy dispersive X-ray (EDX), high resolution transmission electron microscopy (HR-TEM), Raman spectroscopy (RS), ultraviolet-visible spectroscopy (UV-Vis.) and photoluminescence (PL) spectroscopy techniques. The rGO has a sharp 2D peak compared to GO. The sharp nature of 2D band may be due to the larger contribution from single layer sheet. The photocatalytic activity of the synthesized samples has been investigated under UV irradiation. The results of photocatalytic measurements revealed that ~80% of MB dye is degraded by adding the rGO-CdO nanocomposites as photocatalysts into the dye solution. The decrease in the intensity of emission peaks indicates that the photogenerated charge carriers have been transferred from CdO NPs to rGO sheets, which causes to increase the density of O2(-) and OH radicals in the dye solution. The CdO nanoparticles gown on the rGO sheets showed enhanced ferromagnetism (FM) at room temperature, which may be attributed to the short range magnetic interaction of magnetic moments of CdO NPs and spin units present on the rGO sheets.

One-step in situ synthesis of CeO2 nanoparticles grown on reduced graphene oxide as an excellent fluorescent and photocatalyst material under sunlight irradiation.

CeO2 nanoparticles (NPs) with average particle size of ∼17 nm were grown on graphene sheets by simply mixing cerium chloride as the Ce precursor with graphene oxide (GO) in distilled water and the simultaneous reduction of GO to reduced graphene oxide (rGO), followed by a one-step hydrothermal treatment at 150 °C. A unique blue to green tuneable luminescence was observed as a function of the excitation wavelength. With this method, significant applications of rGO-CeO2 nanocomposites in many optical devices could be realized. The photocatalytic activity of the as-synthesized CeO2 and rGO-CeO2 nanocomposite was investigated by monitoring the degradation of methylene blue (MB) dye under direct sunlight irradiation. The rGO-CeO2 nanocomposite exhibited excellent photocatalytic activity compared to CeO2 NPs by degrading 90% of the MB dye in 10 min irradiation under sunlight. This property of rGO-CeO2 nanocomposites was ascribed to the significant suppression of the recombination rate of photo-generated electron-hole pairs due to charge transfer between rGO sheets and CeO2 NPs and the smaller optical band-gap in the rGO-CeO2 nanocomposite.

Correction: One step in situ synthesis of CeO2 nanoparticles grown on reduced graphene oxide as an excellent fluorescent and photocatalyst material under sunlight irradiation.

Correction for 'One step in situ synthesis of CeO2 nanoparticles grown on reduced graphene oxide as an excellent fluorescent and photocatalyst material under sunlight irradiation' by Animesh Kumar Ojha et al., Phys. Chem. Chem. Phys., 2015, DOI: .

Direct visual evidence of end-on adsorption geometry of pyridine on silver surface investigated by surface enhanced Raman scattering and density functional theory calculations.

Fourier transform Raman (FT-Raman) spectra of neat pyridine (Py) and surface enhanced Raman scattering (SERS) spectra of Py with silver nanoparticles (AgNPs) solution at different molar concentrations (X=1.5M, 1.0M, 0.50 M, 0.25 M, and 0.125 M) were recorded using 1064 nm excitation wavelength. The intensity of Raman bands at ∼1003 (ν11) and ∼1035 (ν21) cm(-1) of Py is enhanced in the SERS spectra. Two new Raman bands were observed at ∼1009 (ν12) and ∼1038 (ν22) cm(-1) in the SERS spectra. These bands correspond to the ring breathing vibrations of Py molecules adsorbed at the AgNPs surface. The value of intensity ratios (I12/I11) and (I21/I22) is increased with dilution and attains a maximum value at X=0.5M and upon further dilution (0.25 and 0.125 M) it drops gradually. The theoretically calculated Raman spectra were found to be in good agreement with experimentally observed Raman spectra. Both, experimental and theoretical investigations have confirmed that the Py interacts with AgNPs via the end-on geometry.

Size dependent structural, electronic, and magnetic properties of Sc(N) (N=2-14) clusters investigated by density functional theory.

Structural, electronic, and magnetic properties of ScN (N=2-14) clusters have been investigated using density functional theory (DFT) calculations. Different spin states isomer for each cluster size has been optimized with symmetry relaxation. The structural stability, dissociation energy, binding energy, spin stability, vertical ionization energy, electron affinity, chemical hardness, and size dependent magnetic moment per atom are calculated for the energetically most stable spin isomer for each size. The structural stability for a specific size cluster has been explained in terms of atomic shell closing effect, close packed symmetric structure, and chemical bonding. Spin stability of each cluster size is determined by calculating the value of spin gaps. The maximum value for second-order energy difference is observed for the clusters of size N = 2, 6, 11, and 13, which implies that these clusters are relatively more stable. The magnetic moment per atom corresponding to lowest energy structure has also been calculated. The magnetic moment per atom corresponding to lowest energy structures has been calculated. The calculated values of magnetic moment per atom vary in an oscillatory fashion with cluster size. The calculated results are compared with the available experimental data.

Different proton transfer channels for the transformation of zwitterionic alanine-(H2O)(n=2-4) to nonzwitterionic alanine-(H2O)(n=2-4): a density functional theory study.

We report here the various possibilities of proton transfer between the zwitterionic and the non-zwetterionic form of alanine (Ala) via (H2O)(n=2-4) clusters by calculating the transition state structures of zwitterionic alanine (ZAla)-(H2O)(n=2-4) and non-zwitterionic alanine (Ala)-(H2O)(n=2-4) complexes at B3LYP/6-311++G(d,p) and CAM-B3LYP/6-311++G(d,p) level of theory. In order to determine the most feasible channel for proton transfer, the barrier energy corresponding to each channel was calculated. For the transformation of ZAla-(H2O)(n=2) to Ala-(H2O)(n=2), we identified eight channels for proton transfer. The lowest barrier energy (2.57 kcal mol⁻¹) channel, where ZAla-(H2O)(n=2) transforms to Ala-(H2O)(n=2) via triple proton transfer, is said to be the energetically most feasible channel. The values of barrier energy corresponding to the least energy pathway for proton transfer were calculated to be 1.14 and 9.82 kcal mol⁻¹ for n = 3 and n = 4 complexes, respectively, at B3LYP/6-311++G(d,p) level of theory. For complex n = 3, the structure where proton transfer takes place directly from -NH3⁺ to -COO⁻ has the lowest energy pathway. However, the complexes for n = 2 and 3--the channels where proton transferred from -NH3⁺ to -COO⁻ via two water molecules have the lowest barrier energy. For each n, the values of barrier energy calculated at CAM-B3LYP/6-311++G(d,p) level of theory were always less compared those calculated at B3LYP/6-311++G(d,p) level of theory. The value of rate constants corresponding to each proton transfer channel was also calculated.

Synthesis of well-dispersed silver nanorods of different aspect ratios and their antimicrobial properties against Gram positive and negative bacterial strains.

In the present contribution, we describe the synthesis of highly dispersed silver nanorods (NRs) of different aspect ratios using a chemical route. The shape and size of the synthesized NRs were characterized by Transmission Electron Microscopy (TEM) and UV-visible spectroscopy. Longitudinal and transverse absorptions bands confirm the rod type structure. The experimentally recorded UV-visible spectra of NRs solutions were fitted by using an expression of the extinction coefficient for rod like nano structures under the dipole approximation. Simulated and experimentally observed UV-visible spectra were compared to determine the aspect ratios (R) of NRs. The average values of R for NR1, NR2 and NR3 solutions are estimated to be 3.0 ± 0.1, 1.8 ± 0.1 and 1.2 ± 0.1, respectively. These values are in good agreement with those obtained by TEM micrographs. The silver NRs of known aspect ratios are used to study antimicrobial activities against B. subtilis (gram positive) and E. coli (gram negative) microbes. We observed that the NRs of intermediate aspect ratio (R = 1.8) have greater antimicrobial effect against both, B. subtilis (gram positive) and E. coli (gram negative). The NRs of aspect ratio, R = 3.0 has better antimicrobial activities against gram positive than on the gram negative.

Synthesis, growth mechanism and characterization of single crystalline alpha-Fe2O3 spherical nanoparticles.

In the present report, we proposed a simple and efficient method for synthesizing single crystalline alpha-Fe2O3 spherical nanoparticles array into hexagonal dipyramid (HGDP) hierarchical structures using urea as a surface-active agent to control the growth and nucleation of the iron species. Growth mechanisms for the formation of HGDP hierarchical structures have been also proposed. Single crystalline feature, structural morphology and size of the nanoparticles were investigated by X-ray diffraction (XRD), Scanning and Transmission electron microscopy (SEM). The spectroscopic techniques such as; FT-IR, UV-VIS absorption and Raman spectroscopy were used to investigate optical response of the synthesized nanoparticles. Optical energy band gap was calculated to be 2.57 eV and 2.21 eV corresponding to direct and indirect transitions, respectively. The magnetic properties of the single crystalline nanoparticle were also investigated by Vibrating sample magnetometer (VSM) and found that they are weak ferromagnetic in nature. The values of saturation magnetization, remanent magnetization and coercivity were found to be 0.5925 emu/g and 0.1642 emu/g and approximately 1650 Oe, respectively.

Synthesis of superparamagnetic bare Fe3O4 nanostructures and core/shell (Fe3O4/alginate) nanocomposites.

In this article we report about the synthesis of superparamagnetic bare Fe3O4 nanostructures and core/shell (Fe3O4/alginate) nanocomposites by simple low-temperature based method at pH values 5, 9, and 14. The structural morphology and magnetic behavior of Fe3O4 nanostructures and core/shell (Fe3O4/alginate) nanocomposites (Fe3O4/alg NCs) have been investigated by X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and vibrating sample magnetometer (VSM). The particle size was calculated by TEM measurements and it turns out to be ∼10 nm and ∼14 nm for bare Fe3O4 nanoparticle and Fe3O4/alg NCs with core/shell structure, respectively. The magnetic properties of the synthesized products were found to be function of pH at which the synthesis has been done. The synthesized Fe3O4 nanoparticle and Fe3O4/alg NCs were found to be superparmagnetic in nature at room temperature. We observed that the value of saturation magnetization in case of Fe3O4/alg NCs decreases by increasing the pH value.

Raman and DFT study of polar nu(CN) and non-polar nu(C-H) modes of acetonitrile in aqueous Ag nano-colloids.

Raman spectra of acetonitrile (Acn) in different millimolar (mM) concentrations adsorbed on Ag nano-colloids were recorded in the region 2100-3300cm(-1). The nu(CN) and nu(C-H) modes show blue shifts of approximately 3 and approximately 1cm(-1), respectively, when the concentration of Acn in the mixture is increased from 2 to 8mM. The blue shift of nu(CN) and nu(C-H) modes is predominantly because of adsorption of Acn molecules on Ag nano-colloids. The wave number shift and variation of intensity of the nu(CN) and nu(C-H) bands have been discussed in terms of the adsorption geometry, which probably changes from flat-on configuration at lower concentration of Acn to an end-on configuration at higher concentration of Acn. The dephasing of nu(CN) oscillator becomes considerably slower at higher concentration of Acn. The adsorption of Acn molecules on the nano-colloids was simulated using the (B3LYP) method and the basis sets used for Acn molecules and Ag atoms were 6-311++G(d,p) and Lanl2dz, respectively.

pH-dependent Raman study of pyrrole and its vibrational analysis using DFT calculations.

Raman spectra of pyrrole in aqueous medium at different pH values, 2.5, 5.5, 7.5 and 10.5 were recorded in the two spectral regions, 1,040-1,160 cm(-1) and 3,300-3,360 cm(-1) and pH dependence of the linewidth, peak position and intensity of the Raman bands corresponding to the ring breathing and symmetric nu(N-H) stretching modes were examined. A linear pH dependence of the peak positions for the ring breathing mode and a maximum at nearly neutral pH (7.5) for the symmetric nu(N-H) normal mode is observed, whereas the linewidth (FWHM) shows almost no variation with the change of pH. A slight decrease in the wavenumber position of the nu(N-H) mode at pH value >7.5 indicates that the influence of deprotonation is small, which results from a weak interaction between the reference molecule and the surrounding environment. The density functional theory (DFT) calculations were made primarily to obtain the optimized geometry and vibrational spectra of pyrrole in the ground electronic state using B3LYP functional and the highest level basis set 6-311++G(d,p). The assignments of the normal modes of pyrrole were made on the basis of potential energy distribution (PED). The calculations were also performed on protonated and deprotonated structures of pyrrole.

A study on adsorption of acetonitrile on gold nanorods by non-resonant Raman measurements and density functional theory calculations.

Adsorption of acetonitrile (Ac) molecules on gold (Au) nanorods has been investigated by Raman spectroscopic measurements and density functional theory (DFT) calculations. DFT calculations provide a valuable insight into the underlying structure of the metal-molecule complex. From the best agreement between the observed and the calculated Raman frequencies and also from other spectroscopic observations, we propose that Ac molecules interact with Au nanorods and form an [Ac+2Au](0)-like complex on the surface of nanostructures. The environmental effect has also been taken into consideration to explain the Raman activity of the complex.