Molecular modeling of 4-methylphthalonitrile for dye sensitized solar cells using quantum chemical calculations

The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 4-Methylphthalonitrile was studied based on Hartree-Fock (HF) and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet-visible (UV-Vis) spectrum was investigated by time dependent-density functional theory (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands are assigned to π → π* transitions. Calculated results suggest that three lowest energy excited states of 4-Methylphthalonitrile are due to photo induced electron transfer processes. The interfacial electron transfer between semiconductor TiO₂ electrode and dye sensitizer 4-Methylphthalonitrile is due to an electron injection process from excited dye to the semiconductor’s conduction band. The role of cyanine and methyl group in 4-Methylphthalonitrile in geometries, electronic structures, and spectral properties were analyzed.     

First-principles study of Carbz-PAHTDDT dye sensitizer and two Carbz-derived dyes for dye sensitized solar cells

Dimers of cytosine and its N¹-methylated counterpart were investigated in gas-phase and in various solvents including chloroform, dimethylsulfoxide, and water. The studies were performed at DFT/M06-2X/6-31+G(d,p) level of theory. Relative stabilities of tautomers of cytosine solvated explicitly by a small number of solvent molecules were evaluated. Further solvation effect calculations for homodimers were carried out with conductor-like polarizable continuum model (CPCM). H-NMR shifts and IR frequencies for optimized structures were calculated and compared with available experimental data.     

Donor functionalized quinoline based organic sensitizers for dye sensitized solar cell (DSSC) applications: DFT and TD-DFT investigations

The influence of different donor groups in quinoline based novel sensitizers for dye sensitized solar cell (DSSC) applications is analyzed by using density functional theory (DFT) and time dependent density functional theory (TD-DFT). Quinoline and donor functionalized quinoline based novel organic sensitizers have been designed with different π-spacers for DSSC applications. The ground state molecular structure of novel organic sensitizers is fully optimized by DFT calculation in both gas and chloroform phases. Electronic absorption characteristics are predicted by the TD-DFT calculation in both gas and chloroform phases. The polarizable continuum model is used for solvent phase optimization. The net electron transfer from the donor to acceptor is calculated from natural bond orbital (NBO) analysis. The injection energy and dye regeneration energy values are also calculated. Different donor groups are substituted in quinoline, and these substituted quinoline donors are used as the donor group. Cyanovinyl and thiophene groups act as π-spacers and cyanoacrylic acid acts as an acceptor. DFT and TD-DFT studies of the quinoline and donor functionalized quinoline sensitizers show that the coumarin based and N-hexyltetrahydroquinoline donors are more efficient for DSSC application.     

Structural parameters controlling the performance of organized mesoporous TiO2 films in dye sensitized solar cells

Titanium dioxide films with organized mesoporous structure were investigated as photoanodes in dye sensitized solar cells. High-quality films were grown on FTO supports by implementing the protocol of supramolecular templating with an amphiphilic triblock copolymer, Pluronic P123. Thicker films were obtained by repeated dip-coating and calcination cycles of up to 10 layers. The TiO₂ films were crack-free, optically transparent, and had thicknesses exceeding 2 μm, while still preserving the organized mesoporous morphology. Their roughness factors, determined from Kr-adsorption isotherms, exceeded 500. The sorption of N-3 and N-719 dyes was fitted to a surface coverage of 0.31 molecules/nm², which is about one third of the ideal dye loading assumed for the (1 0 1) anatase face. The solar performance of multilayer films sensitized with N-945 dye scaled linearly for 1-3 layer films, but approached a plateau for thicker films.     

On the performance of ruthenium dyes in dye sensitized solar cells: a free cluster approach based on theoretical indexes

The performance of ruthenium dye sensitized solar cells (DSSC) with different types of ligand was studied by means of a theoretical model where the ruthenium complex is bound to two [Ti(OH)₃]⁺ units, instead of the more usual cluster TiO₂ model. Electron injection is proposed to proceed from a thermalized ³MLCT state rather than from higher vibrational excited states. The efficiency of the dye linked to the two [Ti(OH)₃]⁺ units was determined in terms of a global index (ξ), calculated as the product of three theoretical indexes (F_I) built from the results of time-dependent density functional theory (TDDFT) calculations. The index considers the harvested and delivered energy (F₁), the charge transferred to the semiconductor (F₂), and dye regeneration (F₃). The results show that this set of parameters is unique for each dye, and allows the comparative evaluation of the performance of a series of dyes, with a different ancillary ligand at each stage of the cell operation. The method provides insights that can help explain the improved performance of N3 and black dyes compared to other dyes.

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Graphical abstract Calculated global efficiency for complexes C1–C6. Inset General structure of the interacting model