H.O. Taha

Theoretical characterisation of highly efficient dye-sensitised solar cells

Molecular electronic structure calculations, employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methodologies, have been carried out to improve the performance of the synthesised dye YD2-o-C8 which is characterised by 11.9%–12.7% efficiencies. We aimed to narrow the band gap of YD2-o-C8 to extend the light-harvesting region to near-infrared (NIR). This was done by incorporating Cd instead of Zn onto the porphyrin ring and elongating the length of π-conjugation by adding ethynylene link and anthracene unit, so that the performances of the suggested cells could be expected to exceed the 11.9%–12.7% efficiencies with TiO2, ZnO2, and WO3 oxide electrodes. The effects of modifying the central metal and elongating the length of π-conjugation on cell performance are confirmed in terms of frontier molecular orbital (FMO) energy gaps, density of states (DOS), molecular electrostatic potentials (MEPs), non-linear optical (NLO) properties, ultraviolet–visible (UV–vis) electronic absorption, and 1H nuclear magnetic resonance chemical shifts. Increasing the length of π-conjugation of the D–π–A dyes leads to increasing the DOS near Fermi levels, more active NLO performance, strong response to the external electric field, delocalisation of the negative charges near the anchoring groups, deep electron injection, suppressing macrocycle aggregation, active dye regeneration, and inhibited dye recombination. The calculated band gap/eV of the present DMP-Zn is correlated with the experimental (E1/2(oxidation)–E1/2(reduction)/V) potentials of the identical YD2-o-C8. A co-sensitiser is suggested for NIR sensitisation (550–950 nm) to increase the power-to-conversion efficiency beyond 14%.

Theoretical characterization of axial deformation effects on hydrogen storage of Ti decorated armchair (5,5) SWCNT

Theoretical calculations have been performed in the framework of density functional theory to characterize the effect of axial deformation on hydrogen storage of Ti decorated armchair (5,5) SWCNT. The theoretical characterization has been carried out in terms of H2 adsorption energies that are lying in the desirable energy window (−0.2 to −0.6 eV) recommended by DOE, as well as a variety of physicochemical properties. A remarkable and significant change in H2 adsorption energy is observed under the effect of only (1%) axial strain. Axial relaxation leads to H2 adsorption energies within the recommended energy range for hydrogen storage, in contrast to axial compression. Simultaneous weakening of π and σ interactions, due to the effect of axial relaxation and loss of spatial orbital overlap, is in favor of hydrogen adsorption in the recommended energy range, and dominates the effect of charge transfer from Ti 3d to C 2p of the SWCNT. The calculated pairwise and non pairwise additive components confirm that the role of the SWCNT is not restricted to supporting the metal. Polarizability and hperpolarizabilty calculations as well as spectral analysis characterize the relaxed structure (Z = 1.02), for which H2 adsorption energy (−0.34 eV) is in the recommended energy range for hydrogen storage, to be energetically more preferable than the compressed structure (Z = 0.99). The results offer a way to control and characterize the hydrogenation process of metal functionalized SWCNTs by strain loading.

Theoretical characterisation of irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene

An attempt has been made to characterise the irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene by using the state of the art density functional theory calculations. The single Ni atom prefers to bind at the bridge site between two hexagonal rings of C60 fullerene, and can bind up to four hydrogen molecules with average adsorption energies of −0.85, −0.83, −0.58, and −0.31 eV per hydrogen molecule. No evidence for metal clustering in the ideal circumstances and the hydrogen storage capacity is expected to be as large as 8.9 wt%. While the desorption activation barriers of the complexes nH2NiC60 (n = 1, 2) are outside the desirable energy window recommended by the department of energy for practical applications (–0.2 to –0.6 eV), the desorption activation barriers of the complexes nH2NiC60 (n = 3, 4) are inside this window. The irreversible 2H2 + NiC60 and reversible 3H2 + NiC60 interactions are characterised in terms of several theoretical parameters such as: (1) densities of states and projected densities of states, (2) pairwise and non-pairwise additivity, (3) infrared, Raman, and proton magnetic resonance spectra, (4) electrophilicity, and (5) statistical thermodynamic stability.

Density functional theory study of hydrogen storage on Ni-doped C59X (X = B, N) heterofullerene

ABSTRACT Hydrogen storage reactions on Ni − C59X(X  =  B, N) heterofullerene are investigated by using the state-of-the-art density functional theory calculations. The Ni atom prefers to bind at the bridge site between two hexagonal rings, and can bind up to five hydrogen molecules with average adsorption energies of (−0.94, −0.48, −0.33, −0.25 and −0.20 eV) per hydrogen molecule for Ni − C59B, while (−1.20, −0.60, −0.41, −0.28 and −0.23 eV) per hydrogen molecule for Ni − C59N. With no metal clustering, the system gravimetric capacities are expected to be as large as 10.87 and 10.85 wt % for 5H2NiC59B and 5H2NiC59N, respectively. While the desorption activation barriers of the complexes 1H2 + C59X (X  =  B, N) are outside the Department of Energy domain (−0.2 to −0.6 eV), the desorption activation barriers of the complexes nH2 + C59X(X  =  B, N)(n = 2 − 5) are inside this domain. The hydrogen storage of the irreversible 1H2 + NiC59X (X  =  B, N) and reversible 2H2 + NiC59X (X  =  B, N) interactions is characterised in terms of density of states and projected densities of states, pairwise and non-pairwise additivity, infrared, Raman, electrophilicity and molecular electrostatic potentials.

Theoretical study of hydrogen storage reactions on nickel-decorated heterofullerene C58 BXNY (X + Y = 2)

ABSTRACT In the present study, hydrogen storage reactions on and heterofullerene are investigated by using the density functional theory (DFT) calculations. The atom prefers to bind at the bridge site between a six-membered ring of and between a five-membered and six-membered ring for , and can bind up to six hydrogen molecules with adsorption energies in the range of (−1.06, −0.31 eV) for and (−1.07, −0.33 eV) for , while (−0.86, −0.2 eV) for per hydrogen molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 12.75, 12.77 and 12.74 wt% for , and , respectively. While the desorption activation barriers of the complexes and with is outside the Department of Energy domain (−0.2 to −0.6 eV), and with are inside this domain. For with is outside the DOE domain, and with are inside this domain. The hydrogen storage of the irreversible , , and and reversible , and interactions are characterised in terms of density of states, pairwise and non-pairwise additivity, infrared, Raman (R), electrophilicity and molecular electrostatic potentials. GRAPHICAL ABSTRACT

Theoretical design of highly efficient porphyrazine solar cells

Density functional theory and time-dependent density functional theory methodologies have been applied to design porphyrazine (tetraazaporphyrin) sensitizers. This was done by replacing the porphyrin macrocycle cavity with a porphyrazine macrocycle cavity and increasing the number of p-carboxyphenyl moieties at the macrocycle periphery so that the performances of the suggested cells could be expected to exceed the efficiency of the reference YD2-o-C8 porphyrin sensitizer with Ti38O76, (TiO2)60, SiC, ZrO2, and GaP semiconductor electrodes. Macrocycle replacement assists in promoting the efficiency in the red shoulder of the spectrum more effectively than increasing the number of anchoring groups. The expected effects of the former structural modifications on cell performances are confirmed in terms of natural transition orbitals, energy gaps, semiconductor valence bands and conduction band edges, density of states, UV–visible absorption, and lifetimes of the excited states ΦLHE, Φinject., and ΔGregen. The structural modifications resulted in charge-separated states, unidirectional charge transfer, narrower band gaps, increase of density of states nearby Fermi levels, delocalization of the negative charges near the anchoring groups, efficient light harvesting and electron injection, suppressing macrocycle aggregation, active dye regeneration, and inhibited dye recombination. Co-sensitizers are suggested for near-infrared sensitization.