Energy Levels Of Dyes Research Articles

Electronic structures and photovoltaic properties of a novel phthalocyanine and titanium dioxide phthalocyanine for dye sensitized-solar cells

In the present work, geometries, electronic structures, photovoltaic and optical properties have been carried out on a series of structures formation of phthalocyanine and Titanylphthalocyanine dyes, which are replaced by several subgroup. A density functional theory (DFT) approach together with hybrid function (B3LYP) at SDD basis set was used for the ground state properties in the gas phase. The time-dependent density functional theory (TD-DFT)/ B3LYP was used to investigate the excitation properties of new dyes and analyzed the trends in their optical and redox characteristics. Theoretical principles of HOMO and LUMO energy levels of dyes is requisite in analyzing organic solar cells, thus, HOMO, LUMO levels, open circuit voltage, energy gap, light harvestings efficiency, electron regeneration and electron injection have been calculated and discussed. The outcome of the efficiency, the considered dyes explain absorption energy and wavelength properties that correspond to the solar spectrum requirements. According to results, all the considered materials have a good property and possibility of electron injection procedure from the dyes to conduction band of TiO2, PC60BM or PC60BM. As a result, the molecular changes affect the electronic properties of dye molecules for solar cells. Also, a study of new dyes sensitizers showed that designed materials will be excellent sensitizers. Theoretical designing will prae a way for experimentalists to synthesize the efficient sensitizers for solar cells clearer.

The investigation of novel D-π-A type dyes (MK-3 and MK-4) for visible light driven photochemical hydrogen evolution

Two novel donor-π-acceptor (D-π-A) semiconductor organic dyes have been synthesized for the photochemical hydrogen evolution reaction (HER) to sensitize TiO2 for the first time. The molecular structures of D-π-A semiconductor organic dyes, which are entitled as MK-3 and MK-4, have been characterized by NMR spectroscopy method; and also electrochemical and optical properties have been investigated by cyclic voltammetry and UV–Vis absorption techniques, respectively. Amount of dye loading on TiO2 surface has been investigated by EDX method. The HER activities have been explored in the presence of triethanolamine (TEOA) as a electron donor reagent under sunlight (solar simulator illumination limited by cut-off filter λ ≥ 420 nm) in the absence and presence of co-catalysts (Pt and Cu2WS4). Transient photocurrent densities of MK-3/TiO2 and MK-4/TiO2 electrodes have been reached to 110 μA cm−1 and 275 μA cm−1, respectively. The photocatalytic HER activities have been relatively enhanced in the presence of the Pt or Cu2WS4 co-catalysts (dye/TiO2/Cu2WS4 or dye/TiO2/Pt) when compared to only dye/TiO2. The HER rates have been found as 427, 1277, 675, 682, 1027 and 795 μmolg−1h−1 for the MK-3/TiO2, MK-3/TiO2/Pt, MK-3/TiO2/Cu2WS4, MK-4/TiO2, MK-4/TiO2/Pt and MK-4/TiO2/Cu2WS4, respectively. The differences of photochemical activities of MK-3/TiO2 and MK-4/TiO2 have been stated taking into account dye molecule structures. Moreover, the HER mechanism have been described by using electrochemical band energy levels of dyes, TiO2 and Cu2WS4 co-catalyst.

Interface Electrostatics of Solid-State Dye-Sensitized Solar Cells: A Joint Drift-Diffusion and Density Functional Theory Study

Dye-sensitized solar cells (DSCs) have gained great attention in recent years due to their low-cost fabrication, flexibility and high power conversion efficiency. In a DSC, due to interfaces between the dye and the charge transport materials, the interface electrostatics becomes a key factor determining the overall performance of the cell. Liquid electrolyte based DSCs suffer low stability, electrolyte leakage and in some cases electrode corrosion. Replacing liquid electrolyte with a solid semiconducting material leads to poor interfacial contacts, hence the interface electrostatics becomes one of the limiting factors. In this work, we present a drift-diffusion (DD) and density functional theory (DFT) study of solid-state DSCs to investigate the electrostatics at the TiO2/organic dye/Spiro OMeTAD interface, and its impact to the adsorbed dye energy levels, its absorption spectrum and the related charge injection. In our 3D drift-diffusion model, we solve a set of drift-diffusion equations coupled to Poisson equation for electrons, holes, doping impurities and the interface traps simultaneously. After that, we use first principles DFT modeling of dye-sensitized interfaces in the presence of the calculated electric fields. We find that interface traps located below the conduction band edge of mesoporous TiO2 influence the accumulation of photogenerated holes and built-in electric field near the interface. The built-in electric field leads to change the energetics at the dye/TiO2 interface leading to poor charge injection from excited dye into the TiO2. The simulations were carried out for different electronic trap density in TiO2 and different doping levels in the Spiro OMeTAD hole transport layer. This study helps to a better understanding of interface electrostatics and its role in the charge injection mechanism of solid-state DSCs.

Systematic Study of the Effect of Auxiliary Acceptors in D–A′−π–A Sensitizers Used on Dye-Sensitized Solar Cells

We perform a systematic quantum chemical investigation to elucidate the effect of auxiliary acceptors (A′) on the electronic properties of D–A′−π–A dyes used in dye-sensitized solar cells. A large set of dyes (380) are considered to achieve robust conclusions. Our calculations indicate that the auxiliary acceptor modulates, as expected, the lowest unoccupied molecular orbital level of the dye, except for very poor acceptors. More surprisingly, some auxiliary acceptors also modify the highest occupied molecular orbital level of the dye and its excited states effectively act as auxiliary donors as well. The study of the data set reveals that the effect of changing the π-bridges is highly systematic and predictable. Despite the variability in the geometry between the connected fragments, the frontier molecular orbital energy levels of dyes are very closely related to the energy levels of the component fragments, e.g., it is easy to predict the change in the electronic structure of a dye due to the change of ...

A new method to evaluate the feasibility of a dye in DSSC application

Search for better photo sensitizers has always been a challenge in the field of dye sensitized solar cell (DSSC). This paper suggests a new method to identify a good dye for DSSC through the evaluation of energy levels of dye–TiO2 complex. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the complex are evaluated using cyclic voltammetry (CV) and spectroscopic technique. These energy levels have been used to predict the performance of the solar cell even without fabricating a cell. The authenticity of this method is also revalidated through the correlation of efficiency of practical cell. Copyright © 2017 John Wiley & Sons, Ltd.

Co-Adsorbent Effect on the Sensitization of TiO2 and ZnO Surfaces: A Theoretical Study

Co-adsorbents are often employed in DSSC to avoid electron/hole recombination at the hybrid organic/inorganic interface. Here we investigate, by means of density functional theory simulations, the changes induced in the structural and electronic properties of a hybrid heterostructure by the presence of a co-adsorbent. In particular, we focus on a prototype interface obtained by co-grafting a dye molecule (the hemi-squaraine dye) and imidazole at the oxide surfaces mostly employed in DSSC (anatase-TiO2(101) and ZnO(1100)). Our results show that beside avoiding dye aggregation, the co-adsorbent plays an active role in stabilizing the binding between the chromophore and oxide substrate and in tuning the optoelectronic properties of the system. We found that imidazole shifts downward the dye energy levels (HOMO and LUMO) while raising the oxide valence and conduction bands, strongly influencing the energy alignment of the interface. As such, a co-adsorbent can either modify the type of heterostructure (stradd...

How to Optimize the Interface between Photosensitizers and TiO2 Nanocrystals with Molecular Engineering to Enhance Performances of Dye-Sensitized Solar Cells?

In this work, the interfacial properties of a series of metal-free organic naphthodithienothiophene (NDTT)-based photosensitizers adsorbed on TiO2 surfaces were investigated by a combination of ab initio calculations and experimental measurements. The calculations and experiments reveal that because of the efficient charge transfer from the adsorbed dyes to TiO2 nanocrystal surface there is an upward shift for the energy levels of dyes and a downward shift for the conduction band of surface TiO2 and that the band gaps for both of them are also reduced. Such electronic level alignments at the interface would lead to increased light absorption range by adsorbed dyes and increased driving force for charge injection but reduced open-circuit potential (V(oc)). More interestingly, we found that molecule engineering of the donor group and introducing additional electron-withdrawing unit have little effect on the electronic level alignments at the interface (because band gaps of the dyes adsorbed on TiO2 surfaces become approximately identical when compared with those of the dyes measured in solution) but that they can affect the steric effect and the charge separation at the interface to tune V(oc) and the short-circuit current density (J(sc)) effectively. All these findings suggest that optimizing the interfacial properties of dyes adsorbed on TiO2 surfaces by synchronously modifying steric effects of dye molecules anchored on TiO2 and charge-transfer and separation properties at the interfaces is important to construct efficient dye-sensitized solar cells.

Atomic-Scale Observation of Multiconformational Binding and Energy Level Alignment of Ruthenium-Based Photosensitizers on TiO2Anatase

Dye-sensitized solar cells constitute a promising approach to sustainable and low-cost solar energy conversion. Their overall efficiency crucially depends on the effective coupling of the photosensitizers to the photoelectrode and the details of the dye's energy levels at the interface. Despite great efforts, the specific binding of prototypical ruthenium-based dyes to TiO2, their potential supramolecular interaction, and the interrelation between adsorption geometry and electron injection efficiency lack experimental evidence. Here we demonstrate multiconformational adsorption and energy level alignment of single N3 dyes on TiO2 anatase (101) revealed by scanning tunnelling microscopy and spectroscopy. The distinctly bound molecules show significant variations of their excited state levels associated with different driving forces for photoelectron injection. These findings emphasize the critical role of the interfacial coupling and suggest that further designs of dye-sensitized solar cells should target a higher selectivity in the dye-substrate binding conformations in order to ensure efficient electron injection from all photosensitizers.

A Comparison of Indoline Dyes as Photosensitizers in Dye-Sensitized Solar Cells

Properties of four indoline dyes were studied by means of density functional theory (DFT) and time- dependent density functional theory (TD-DFT) with the goal of finding an excellent photosensitizer for use in dye-sensitized solar cells. Theoretical results showed that the frontier molecular orbital structures of indoline dyes are suitable for electron injection from the excited states of indoline dyes to a TiO2 electrode. Calculated UV-visible absorption spectra of indoline dyes in vacuum match well with solar radiation spectra. The calculated energy levels of these dye molecules demonstrate that indoline dyes can be used as photosensitizers for TiO2 nanocrystalline solar cells together with the I-/I3- electrolyte. The lowest unoccupied molecular orbital (LUMO) energy levels of indoline dyes are higher than the conduction band edge of the TiO2 crystal, which ensures a high efficiency of electron transfer from indoline dyes to TiO2 electrodes. As the highest occupied molecular orbital (HOMO) energy levels of indoline dyes are lower than those of I-/I3- , molecules that donated electrons can receive electrons from the electrolyte. By comparison with the experimental data, the transfer efficiency of dye-sensitized solar cells may be determined mainly by the LUMO energy levels. The working lifetime of a dye-sensitized solar cell depends mainly on the stability of the dye molecule. From an analysis of the bond length of chemical bonds, we find that the stability of the four indoline dye molecules is basically the same. We further show that indoline dye 1 (ID1) has the highest LUMO energy level and the highest molecular stability. Its absorption spectra match solar radiation spectra well in an ethanol solution, therefore, it is the best photosensitizer among the analyzed dyes for application in dye-sensitized solar cells.

インクジェットプリンティング用高耐久性染料の開発と工業的製造法の確立

Water-soluble novel cyan and magenta dyes, which show high light-fastness and ozone-fastness on porous photo media, have been invented for ink jet printing system. Control of dye energy levels, removal of sensitive groups towards ozone, and acceleration of copper-phthalocyanine complex (CuPc) aggregation were the dominant factors to improve both ozone-fastness and light-fastness significantly. For the development of the CuPc cyan skeleton, alkyl sulfonyl groups, all of which were located at beta positions on the CuPc skeleton, were effective to improve fastness. For the development of the magenta skeleton, the combination of aniline-substituted pyridine coupling component and pyrazole diazonium component was inherently important skeleton to improve fastness.Regarding the production process of the novel CuPc dye, solvent effect, control of pH and dehydration reagent such as an orthoester were the dominant parameters to improve cyclization yield. In the novel magenta dye, both introduction of plural functional groups at the same time and development of a highly regioselective reaction for sulfonation were key synthetic processes to establish a successful synthetic route.

Molecular design of coumarin dyes with high efficiency in dye-sensitized solar cells

Density functional theory (DFT) and time-dependent DFT calculation have been applied to study the coumarin dyes which act as photosensitizer in dye-sensitized solar cells. The absorption spectra of coumarin dyes in ethanol can be well reproduced with theoretical method. The outstanding performance of NKX-2311 roots in higher light harvesting efficiency and more efficient electron injection efficiency into conduction band of TiO 2 electrode according to our computation. Absorption peaks and HOMO energy levels of dyes can be employed as the two effective theoretical parameters for the judgement of their solar to energy efficiency. New coumarin dyes which probably possess higher efficiency were designed referring to our conclusions.

On the use of cyanine dyes as low-bandgap materials in bulk heterojunction photovoltaic devices

Cyanine dyes with absorption edges of almost 1000 nm were used in combination with MEH-PPV for the fabrication of organic solar cells. For blended thin films, a pronounced phase separation between the two components occurred and resulted in photocurrents with different signs for bilayer and bulk heterojunction devices. Absorption spectra and selective dissolution experiments were used to illustrate the process of vertical phase segregation, with the preferential wetting of the polar anode by the cyanines while maintaining percolating carrier pathways between the electrodes. For a cyanine with long alkyl side chains, the compatibility with the polymer matrix was increased and the development of the effective inverted bilayer configuration was not observed. The generally low oxidative photocurrents were explained with unfavourable shifts of the highest occupied molecular orbital (HOMO) dye energy levels in the solid state.

Sensitization effect in doped and undoped state of polypyrrole by methylene blue in solid state electrochemical cells

Methylene blue (MB) at small concentration is used as a photosensitizer in the solid state photoelectrochemical cells fabricated using doped and undoped polypyrrole (Ppy) coated electrodes sandwiched with solid polymer electrolyte (SPE) viz. polyvinylalcohol (PVA) doped with phosphoric acid. Different sensitization effects are observed for the same polymer–dye combination. MB sensitizes Ppy in doped state more efficiently as compared to undoped state of the polymer. The actual placement of the energy levels of dye with respect to polymer and ease with which polymer transports photogenerated charge carriers without recombination are observed to be important in such sensitization processes and governs the overall process.

Dye desensitization studies: AgBr core—shell versus AgBr core—AgIBr shell emulsions

Four 0.73 μm core-shell octahedral emulsions, sulphur-plus-gold sensitized either internally or on the surface, were used to study dye desensitization by anionic J-aggregating dyes. Two of the emulsions were pure AgBr and two contained AgBr cores with AgI0.01Br0.99 shells. Four dyes having a systematically varying electrochemical oxidation potential, Eox, were studied at 20, 40, 60, 80 and 100 per cent monolayer coverage. None of the dyes desensitized the internal image of either emulsion. However, desensitization of the surface-sensitized emulsions was observed, particularly for the dyes with Eox less than about 1.1 V (versus Ag/AgCl in acetonitrile), and it was greater for the iodobromide surface. Photobleaching studies showed that the dye bleaching rate was greater on the iodobromide surface. Spectral speeds for internal image formation as a function of dye coverage agreed with predicted speeds obtained from integrated absorption spectra for three of the dyes. However, the dye whose lowest unoccupied molecular orbital (LUMO) was the lowest in energy of all four dyes only agreed with the predicted spectral speed at lower dye coverages. Deviation from predicted spectral speed at higher dye coverage for this dye was attributed to the mean of its LUMO energy-level distribution being near the bottom of the conduction band. At low dye coverages formation of J-aggregates near ‘special sites’ populated the upper levels of this distribution, but additional aggregates formed at higher dye coverages populated the lower levels of the distribution. The higher desensitization for dyes adsorbed to the iodobromide surface suggested that the dye energy levels lie higher in energy on this surface than on the AgBr surface.

EoC21a. Photoconducting ferroelectric polymers

Abstract The new photoconducting ferroelectric polymer is prepared by means of dye sensitization of ferroelectric vinylidene fluoride-trifluoroethylene copolymers P(VDP-TrFE). The photoconductivity, the bulk photovoltaic effect and photochromic effect have been observed in the spectral bands connected with dye molecules absorption. The new photoconducting ferroelectric polymer may be used as the photorefractive material. By means of the photochromic effect in the ferroelectric copolymer doped by indolynospiropyran the transmission gratings were received. At the ferroelectric phase transition the sharp changes of the dye energy level and oscillator strength are revealed.

Absorption changes at the phase transition of ferroelectric copolymers doped by a cyanine dye

Abstract At the ferroelectric phase transition in the optically sensitized ferroelectric vinylidene fluoride-trifluorethylene copolymers P(VDF-TrFE) the sharp change of the dye energy level and optical absorption is revealed. In ferroelectric P(VDF-TrFE) copolymer doped by cyanine due to the structural chromic effect is observed, which characterized by the reversible change of the film color at the ferroelectric phase transition.

Optical sensitization at the phase transition in the ferroelectric vinylidene fluoride-trifluoroethylene copolymer

At the ferroelectric phase transition in the optically sensitized ferroelectric vinylidene fluoride-trifluoroethylene copolymers P(VDF-TrFE) the sharp change of the dye energy level is revealed. In ferroelectric P(VDF-TrFE) copolymer doped by indolynospiropyran the structural chromic effect is observed, which is characterized by the reversible change of the film color at the ferroelectric phase transition.

Structural chromic effect in the optically sensitized ferroelectric polymers

Abstract At the ferroelectric phase transition in the optically sensitized ferroelectric vinylidene fluoride-trifluoroethylene copolymers P(VDF-TrFE) the sharp change of the dye energy level is revealed. In ferroelectric P(VDF-TrFE) copolymer doped by indolynespiropyran the structural chromic effect is observed, which is characterized by the reversible change of the film colour at the ferroelectric phase transition.

Effect of Dye Energy Level on the Efficiency and Energetics of Spectral Sensitization

AbstractA series of dyes varying widely in their lowest vacant (LV) and highest occupied (HO) levels were used to study the effect of dye energy level on the efficiency and energetics of spectral sensitization of an iridium-doped Ag(I)Br emulsion. Results from room-air sensitometry and vacuum sensitometry at various temperatures formed a data base on which to assess current theories of spectral sensitization. The oxygen/moisture sensitivity of the spectral response showed an energy-level threshold in concentration dependence. As the dye LV level was farther displaced from the vacuum level, the dye relative quantum efficiency decreased and the spectral activation energy increased, both linearly. Dyes that failed to follow the general trends were strongly aggregating dyes with low LV levels. Quantitative predictions of the direct-electron-transfer model of spectral sensitization were inconsistent with the results.

Theoretical analysis of S1-state lifetime measurements of dyes with picosecond laser pulses

Various methods for the determination of the S1-state lifetime of dye solutions (laser dyes and modelocking dyes) are analysed. A general model of interaction of laser light with dye molecules is presented and reduced to a dye energy level scheme of six levels. Fluorescence emission, light amplification and absorption recovery techniques are investigated theoretically and their limitations revealed. The determination of the S1-state lifetime of saturable absorbers by single picosecond pulse bleaching experiments is very thoroughly discussed. The influence of various laser and dye parameters on the bleaching experiments are analysed numerically. The results are compared with isotropic steady state two- and three-level dye models.