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Calculations based on second-order Moller-Plesset and density functional theory (DFT) methods using different exchange and correlation functionals are performed on C 2 H 4 Nb organometallic complex for its hydrogen storage capacity. We found that this complex can store up to a maximum of 14 H 2 molecules using Becke-3 Lee-Yang-Parr (B3LYP)/LanL2DZ method, with a gravimetric H 2 uptake capacity of 18.92 wt% and average binding energy of 0.52 eV/H 2 . The evaluation of the temperature dependence of the Gibbs free energy change (DG) of H 2 adsorption process indicates that the adsorption of H 2 molecules is energetically favorable below 250 K using B3LYP (LanL2DZ) and PBEPBE (LanL2MB, LanL2DZ) level of theories. On the basis of the DFT descriptors, calculated at B3LYP (LanL2DZ) and B3PW91 (LanL2MB) level of theory, we found that the stability of the complex increases with increase in the number of H 2 molecules adsorbed by the complex.

We report the theoretical modeling of various azo-bridged coumarin-purpurin systems. The effect of varying the donor (coumarin) part of this D-π-D-π-A system was analyzed in terms of opto-electronic and photovoltaic parameters such as HOMO, LUMO, HOMO-LUMO energy gap, λ max , light harvesting efficiency, charge injection efficiency, open voltage, reorganization energy by employing density functional theory as incorporated in Gaussian 03 set of codes. The dye-TiO 2 adsorbed systems were also studied using the same level of theory. It was found that just by varying the donor, although of same nature, there is a marked effect on the efficiency parameters of the dye sensitized solar cells based on such dyes. Also, the dye molecules were found to be good sensitizers for TiO 2 semiconductors. K E Y W O R D S DFT, DSSC, light harvesting efficiency, optoelectronic, photovoltaic parameters | INTRODUCTIONDue to the over exploitation of the natural resources coupled with the increasing levels of pollutions, there is immediate need to develop some alternative, clean resources of energy. In this regard, solar energy is the easily available and clean form of energy that can be well harnessed to meet our present as well as future energy demands. To convert this solar energy into usable forms we have some devices called photovoltaic solar devices and amongst them dye sensitized solar cells (DSSC) are better options, owing to their easy manufacture, cost effectiveness, and flexibility.With the advent of the DSSC technology the conversion of the solar energy to electricity became cheap than the traditional silicon-based photovoltaics. [1,2] Amongst DSSCs, those based on organic dye sensitizers have been found to be advantageous owing to their easy synthesis and low cost. The study of these organic metal free dye sensitizers for DSSCs are important as they have paved the way for designing DSSCs with better efficiencies in a cost effective manner. Organic dyes have exhibited higher conversion efficiencies up to 12.5% for carbazoles and indenoperylene electron-donor based dye sensitizers while as 12.8% efficiency has been achieved for triphenylamine-based dye using cobalt-based electrolyte system. [3,4] Amongst the organic sensitizers, those based on push-pull framework or donor-π-acceptor (D-π-A) form are worth mentioning These push-pull dye molecules are very promising due to their high molar extinction coefficient, cost effectiveness, and diversity. [5][6][7][8][9] Along with experimental studies, a number of theoretical researches have been carried out on various organic dyes. The theoretical studies have served as a tool for verifying the results found experimentally. As such, number of such studies has been carried out, such as those based on coumarins [10][11][12][13][14][15][16] and triphenylamine. [17][18][19][20] Theoretical studies by several researchers [15,[21][22][23][24][25] on NKX coumarin derivatives have been carried for understanding the relationship between the molecular properties of these dye sensitizers and the...

We report DFT studies on some perylene-based dyes for their electron transfer properties in solar cell applications. The study involves modeling of different donor-p-acceptor type sensitizers, with perylene as the donor, furan/pyrrole/thiophene as the p-bridge and cyanoacrylic group as the acceptor. The effect of different p-bridges and various substituents on the perylene donor was evaluated in terms of opto-electronic and photovoltaic parameters such as HOMO-LUMO energy gap, k max , light harvesting efficiency(LHE), electron injection efficiency (Ø inject ), excited state dye potential (E dye *), reorganization energy(k), and free energy of dye regeneration (DG Regen dye ). The effect of various substituents on the dye-I 2 interaction and hence recombination process was also evaluated. We found that the furan-based dimethylamine derivative exhibits a better balance of the various optical and photovoltaic properties. Finally, we evaluated the overall opto-electronic and transport parameters of the TiO 2 -dye assembly after anchoring the dyes on the model TiO 2 cluster assembly. K E Y W O R D S donor-p-acceptor dyes, dye sensitization, electron injection efficiency, light harvesting efficiency, solar energy, titanium dioxide nano compositesThe extensive exploitation of energy resources, and the associated environmental crisis such as climate change caused by the increasing consumptions of fossil fuels, is a matter of serious concern which needs immediate attention. Energy resources, especially petroleum, coal, and natural gas, which constitute the major share of the available natural resources, are being extensively consumed by the growing population and their unabated use is adding to the global warming. The situation is alarming and demands the development of alternative clean forms of energy which, along with solving the problem of energy crisis will also address the pollution problems; thereby cutting down the global warming. In recent years, solar energy has been considered as a promising alternative to the conventional resources, since it is easily available and constitutes a clean form of energy. Considerable attention has been devoted to the manufacturing of efficient solar light harvesters which are complementary to the silicon-based solar devices but with enhanced light harvesting efficiency. In this category, dye sensitized solar cells (DSSCs) are considered as pioneer candidates due to their better light harvesting ability, low cost, and maximum efficiency in comparison to the traditional silicon-based solar devices. [1-4] The development of a highly efficient solar cell by Gratzel et al. was achieved by the sensitization of a TiO 2 nanocomposite by ruthenium-based molecular dyes which have reached the power conversion efficiency of around 7-12%. [5-10] The ruthenium(II)bipyridyl systems have been considered as the most efficient systems in terms of photo-conversion efficiency;however, the record is still held by a zinc-based porphyrin dye exhibiting a conversion efficiency of 12.3%. [11] A DSSC can b...

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