Dye Sensitizers For Solar Cells Research Articles

Study of Geometrical, Electronic Structure, Spectral, and NLO Properties of Phenyl‐Based Azo Dyes of Dye Sensitizer for Solar Cells: A Theoretical Study

AbstractThe molecular geometry, electronic structure, and absorption spectra of some important phenyl derivatives are investigated by using DFT and TD‐DFT with B3LYP and CAM‐B3LYP functional. The highest HOMO–LUMO energy gap, Non‐linear optical properties of dipole moment, polarizability, and hyperpolarizability are calculated. In both methods hyperpolarizability PDP values (16.77 × 10−30 and 16.59 × 10−30 esu) are higher than PDNA, PDN, and MPAN dye. The Molecular electrostatic potential shows that PDNA dye has more electronegative potential. Comparing all the dyes, PDP dye shows a higher light harvesting efficiency in the UV–vis region. The vibrational frequencies are assigned based on the potential energy distribution (PED) using the VEDA‐4 program.

Influence of a One-Pot Approach on a Prepared CuS Macro/Nanostructure from Various Molecular Precursors

Nanostructured metal sulfides such as copper sulfide (CUS) form from single-source precursors (SSPs) and are cost-friendly materials that can be used in a one-pot approach with potential applications in dye-sensitizer solar cells (DSCs). This is an attractive pathway that allows the careful control of tailoring the design of the nanostructures with slight variations in the mixture conditions to form uniform nanoparticles and enhance the performance of DSCs. We report on the optical, structural, and morphological properties of CuS as photosensitizers and their application in QDSCs using characterization techniques such as cyclic voltammetry (CV), current–voltage (I-V), UV-Vis spectroscopy (UV-Vis), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), etc. The UV-Vis reveals that the band gap for the three samples is found at 2.05–2.87 eV, confirming them as suitable materials for solar cells. The XRD peaks for the three CuS nanoparticles harmonized very well with hexagonal CuS. The thermal gravimetric (TGA) suitability of the three complexes shows a two-step decomposition within the temperature range of 125–716 °C, with a final residue of 2–4%. CV curves for three samples show that none of the developed metal sulfides exhibits a peak indicative of limited catalytic activity in the iodine electrolyte. The I-V overall energy conversion efficiency (η%) of 4.63% for the CuSb photosensitizer is linked to the wide electronic absorption spectrum and better relative dye loading. The synthesis of photosensitizers from a trioctylphosphine oxide (TOPO) capping agent shows improved efficiency compared to our previous studies, which used hexadecylamine as a coordinating solvent.

Understanding Charge Dynamics in Dense Electronic Manifolds in Complex Environments.

Photoinduced charge transfer (CT) excited states and their relaxation mechanisms can be highly interdependent on the environment effects and the consequent changes in the electronic density. Providing a molecular interpretation of the ultrafast (subpicosecond) interplay between initial photoexcited states in such dense electronic manifolds in condensed phase is crucial for improving and understanding such phenomena. Real-time time-dependent density functional theory is here the method of choice to observe the charge density, explicitly propagated in an ultrafast time domain, along with all time-dependent properties that can be easily extracted from it. A designed protocol of analysis for real-time electronic dynamics to be applied to time evolving electronic density related properties to characterize both in time and in space CT dynamics in complex systems is here introduced and validated, proposing easy to be read cross-correlation maps. As case studies to test such tools, we present the photoinduced charge-transfer electronic dynamics of 5-benzyluracil, a mimic of nucleic acid/protein interactions, and the metal-to-ligand charge-transfer electronic dynamics in water solution of [Ru(dcbpy)2(NCS)2]4-, dcbpy = (4,4'-dicarboxy-2,2'-bipyridine), or "N34-", a dye sensitizer for solar cells. Electrostatic and explicit ab initio treatment of solvent molecules have been compared in the latter case, revealing the importance of the accurate modeling of mutual solute-solvent polarization on CT kinetics. We observed that explicit quantum mechanical treatment of solvent slowed down the charge carriers mobilities with respect to the gas-phase. When all water molecules were modeled instead as simpler embedded point charges, the electronic dynamics appeared enhanced, with a reduced hole-electron distance and higher mean velocities due to the close fixed charges and an artificially increased polarization effect. Such analysis tools and the presented case studies can help to unveil the influence of the electronic manifold, as well as of the finite temperature-induced structural distortions and the environment on the ultrafast charge motions.

Synthesis of Conjugated bis-Schiff Base and Their Complexes as Dye-Sensitizer for Dye Sensitized Solar Cell (DSSC) Application

Schiff base and their metal complexes have been widely used as photovoltaic materials due to their excellent π-electron transfer properties along the molecule. A total of eleven conjugated symmetrical bis-Schiff base and their complexes with different π-spacers have been synthesized and spectroscopically characterized in order to investigate their conversion efficiency in dye-sensitizer solar cells (DSSC). All compounds were either substituted with hydroxy (-OH) or methoxy (-OMe) as the electron donor and difluoro boron (BF2) as the electron acceptor or without any substituent. All compounds were applied as dye-sensitizer in DSSC using titanium (IV) oxide (TiO2) coated on a fluoride doped tin oxide glass as the working electrode and electric paint containing carbon black, whereas graphene coated indium tin oxide glass as the counter electrode. The power conversion efficiencies of the eleven bis-Schiff bases were compared to N3 Dye as the benchmark standard. The results showed that the compound with aromatic ring bridge as the π-spacer and -OMe substituent gave the highest efficiency at 0.0691% whereas the compound with aromatic ring and BF2 gave the lowest efficiency at 0.0012%.

Study of Geometrical, Electronic Structure, Spectral and Nlo Properties of Phenyl Based Azo Dyes of Dye Sensitizer for Solar Cells: A Theoretical Study

Study of Geometrical, Electronic Structure, Spectral and Nlo Properties of Phenyl Based Azo Dyes of Dye Sensitizer for Solar Cells: A Theoretical Study

The chemical reactivity and QSPR of organic compounds applied to dye-sensitized solar cells using DFT

The structural and electronic properties were calculated for seventy organic compounds used as dye sensitizers in solar cells, applying the B3LYP exchange-correlation energy functional with the 6-311G∗∗ basis set. Moreover, the present study proposes two new quantitative structure-property relationship (QSPR) models that enable the prediction of the power conversion efficiency (PCE) and maximum absorption wavelength (λmax) of these systems, the two QSPR models were validated using the coefficient of determination (R2) of 0.62 for both models with the leave-one-out cross-validation correlation coefficient (Q2LOO) of 0.55 and 0.57, respectively. Furthermore, applicability domain analysis was conducted in order to identify the related compounds via the extrapolation of the model.

Fusing Thienyl with N-Annulated Perylene Dyes and Photovoltaic Parameters for Dye-Sensitized Solar Cells.

Due to the role of dyes in dye-sensitized solar cells (DSSCs), designing novel dye sensitizers is an effective strategy to improve the power conversion efficiency. To this end, the fundamental issue is understanding the sensitizer's trilateral relationship among its molecular structure, optoelectronic properties, and photovoltaic performance. Considering the good performance of N-annulated perlyene dye sensitizers, the geometries, electronic structures, and excitations of the selected representative organic dye sensitizers C276, C277, and C278 as well as dyes adsorbed on TiO2 clusters were calculated in order to investigate the relationship between molecular structures and properties. It was found that fusing thienyl to N-annulated perlyene can elevate the highest occupied molecular orbital (HOMO) energy, reduce the orbital energy gap, increase the density of states, expand the HOMO to the benzothiadiazole moiety, enhance the charge transfer excitation, elongate the fluorescence lifetime, amplify the light harvesting efficiency, and induce a red-shift of the absorption spectra. The transition configurations and molecular orbitals of the dye-adsorbed systems support that the electron injection in DSSCs based on these dyes is a fast mode. Based on extensive analysis of the electronic structures and excitation properties of these dye sensitizers and the dye-adsorbed systems, we present new quantities as open-circuit voltage and short-circuit current density descriptors that celebrate the quantitative bridge between the photovoltaic parameters and the electronic structure-related properties in order to expose the relationship between properties and performance. The results of this work are critical for the design of novel dye sensitizers for solar cells.

Stabilization of Mercuric Iodide Using Titanium and Silicon Oxides

Digital x-ray detectors consist of a conversion material, which converts incident radiation to an electrical signal, as well as a read-out circuit that is used to detect the electrical signal. Research is being conducted in order to improve their performance across various fields. In particular, many studies have explored the conversion materials to address the limitations of amorphous selenium (a-Se) currently in use and to develop alternative materials. Mercuric iodide (HgI2) is one of the alternative materials being considered as it has greater x-ray sensitivity than a-Se and other candidate materials. This is due to its high atomic number and high x-ray absorption efficiency. It also had a high rate of electron-hole pair generation per particle due to its low pair creation energy. However, it is difficult to commercialize HgI2 due to its high leakage current and unstable x-ray sensitivity. This study aims to resolve the disadvantages of HgI2 by adding silicone dioxide (SiO2), which is used as oxide film and insulating film in semiconductor processes, and titanium dioxide (TiO2), which is used as an electrode in dye sensitizer solar cells. Detectors are fabricated for analysis using HgI2, HgI2-TiO2, and HgI2-SiO2 unit-cells and the particle-in-binder method. SEM, dark current, and x-ray sensitivity measurements are used to compare their structural characteristics, electrical properties, and stability, respectively.

Photophysical, electrochemical, and DFT studies of the novel azacrown-bridged dinuclear ruthenium dye sensitizers for solar cells

A dinuclear ruthenium bipyridyl complex with 1,10-diaza-18-crown-6 bridging ligand was synthesized and characterized. Its photophysical and electrochemical properties were also studied. DFT computations were performed to complement the experimental investigations. Analysis of the results indicates that the path in which charges move from one metal center to the other is significant for effective electronic coupling. However, electron transfer between the two ruthenium centers is hindered by the azacrown bridging ligand, compared to the smooth electronic transfer reported for a related dye involving an azo bridging ligand.

The bis-dimethylfluoreneaniline organic dye sensitizers for solar cells: A theoretical study and design

Development of novel dye sensitizers with suitable optoelectronic properties is effective to improve the power conversion efficiency of dye-sensitized solar cells (DSSCs). Considering the effectiveness of conjugate bridges in modification of optoelectronic properties, based on the dye sensitizers C201, C203, C204 and C205, five kinds of organic dye sensitizers are designed with different thiophene-based moieties and the functionalized graphene flakes (GFs) as conjugate bridges. The performances of these dye sensitizers are analyzed in terms of the calculated geometries, electronic structures and excitation properties. The transition configurations and molecular orbitals of dye sensitizers suggest that bis-dimethylfluoreneaniline is effective electron donor, and the transitions of optical absorption in visible region are charge transfer excitations. The conjugate lengths, energy level alignments, light harvesting capabilities, excitation character, and transition properties, as well as the free energy variations for electron injection and dye regeneration support that the designed dye sensitizers are effective to be applied in DSSCs. Particularly, introducing the functionalized GF into conjugate bridges significantly elongate conjugate length, reduce orbital energy gap, lead to denser distribution of orbital energy, generate red-shift of absorption spectra, enhance light harvesting capability, increase absorption bands and coefficients. Therefore, introducing the functionalized GF into conjugate bridges is effective, and the designed panchromatic dye sensitizer C20x-GF-BTD must be better than other designed dye sensitizers for DSSCs.

Investigation of effect of batch-separation on the micro-energy generation in M.indica L. dye-sensitized Solar Cells

The technology of silicon panels has improved over the years with the application of silicon into several material architecture. However, the high cost of the technology has limited its wide adoption. Recent advances have shown that natural materials employed as dye sensitizers for solar cells provide viable alternatives at low cost. This study focused on implementing Mango (Magnifera indica Linn.) leaf dye as dye sensitizer for solar cells. Unlike previous approaches, it employed batch-separated M.indica L. to sensitize two groups of dye-sensitized solar cells (DSCs). Parameters such as short circuit current (Isc), open circuit voltage (Voc), maximum power (Pmax), fill factor (ff), incident photon to conversion efficiency (IPCE) and output efficiency (ƞ) were used to determine the outcome of the M.indica L. DSCs. The doctor blade method and high temperature sintering at 450 °C was used in the preparation of both photoanodes. Photovoltaic results reveal DSCs with a higher efficiency of 4.75 x 10-3 % in crude M.indica L. than 0.07 x 10-3 % for batch separated hexane faction of M.indica L. under same conditions of standard air mass. Remarkably, the hexane M.indica L.DSC recorded larger values of Isc and Voc. The significance of this result is that crude M.indica L DSCs are more affordable, have a facile production process and is an ecologically safe alternatives to silicon solar cells. Although the efficiencies are comparatively low, further research with a solar simulator and co-sensitization with other dyes is recommended for a better outcome.

Linear correlation between DSSC efficiency, intramolecular charge transfer characteristics, and NLO properties – DFT approach

Abstract The trends in the dye-sensitizer solar cells (DSSCs) efficiencies of 4 N, N-dimethylaniline-based polyene sensitizers, NKX-2553, NKX-2554, NKX-2600, and NKX-2569 have been correlated with the trends in intramolecular charge transfer characteristics as revealed by the trends in non-linear optical (NLO) properties. Both an electron-donor and π-linkers play a vital role in the performance of the sensitizer/dye in the DSSCs as well as in NLO properties. Optimized geometries showed that the cyanoacrylic acid unit is planar with the π-bridge, including a methine, a thiophene and two methine units, and a donor unit, confirming an extensive an electron transfer. Natural Bond Orbital (NBO) analysis for metal-free organic sensitizer has been shown that the electron transfer occurs from an electron donor (D) to electron acceptor (A) units. Bond length change (BLA) values demonstrate a good relationship with ascertained estimation of second-order hyperpolarizability. The singlet–triplet investigation demonstrates that the sensitizer having a required estimation of the singlet–triplet energy gap, and it is a good contender for the DSSCs application. Frontier molecular orbital (FMO) analysis showed that both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) have electron localization support the electron transfer characters. These results give the direction for optimizing the metal free organic dyes as efficient sensitizers/dyes in Dye-Sensitized Solar Cells (DSSCs) and NLO applications.

Synthesis of carboxylated chlorophyll derivatives and their activities in dye-sensitized solar cells

Chlorophyll-a derivatives possessing a carboxy group in the substituent at the 3-position were prepared by chemical modification of methyl pyropheophorbide-d bearing the 3-formyl group via a Wittig, Barbier-type, or Knoevenagel reaction. The synthetic carboxylated chlorophyll pigments were employed as dye sensitizers for solar cells and their performances were compared in a conventional device based on a mesoporous titanium dioxide electrode and a liquid electrolyte. The solar power conversion efficiency was suppressed with an increase in the length of the oligomethylene moiety between the chlorin π-system and the carboxy group, while a corresponding π-linked ethenylene spacer enhanced the efficiency.

Versatile ruthenium(II) dye towards blue-light emitter and dye-sensitizer for solar cells

A versatile Ru(II) complex bearing an anthracene moiety was synthesized in our search for suitable compounds towards efficient molecular devices. The new engineered dye, cis‑[Ru(dcbH2)(NCS)2(mbpy‑anth)] (dcbH2=2,2′‑bipyridyl‑4,4′‑dicarboxylic acid, mbpy‑anth=4‑[N‑(2‑anthryl)carbamoyl]‑4′‑methyl‑2,2′‑bipyridine), exhibits a blueish emission in a vibronically structured spectrum ascribed to the fluorescence of a 1LCAnth (ligand centered) excited state in the anthracene and has a potential to be exploited in the fields of smart lighting and displays. This complex was also employed in dye-sensitized solar cells with fairly efficient solar energy conversion with the use of self-assembled TiO2 compact layers beneath the TiO2 mesoporous film to prevent meso‑TiO2/dye back reactions. Further photoelectrochemical investigations through incident photon-to-current efficiency and electrochemical impedance spectra showed that the all-nano-TiO2 compact layer acts as contact layers that increase the electron harvesting in the external circuit, enhancing efficiencies up to 50%.

DFT and TD-DFT calculations of metallotetraphenylporphyrin and metallotetraphenylporphyrin fullerene complexes as potential dye sensitizers for solar cells

Density functional theory (DFT) and time-dependent DFT calculations have been employed to model metallotetraphenylporphyrin dyes and metallotetraphenylporphyrin –fullerene complexes in order to investigate the geometries, electronic structures, the density of states, non-linear optical properties (NLO), IR–vis spectra, molecular electrostatic potential contours, and electrophilicity. To calculate the excited states of the tetraphenyl porphyrin analogs, time-dependent density functional theory (TD-DFT) are used. Their UV–vis spectra were also obtained and a comparison with available experimental and theoretical results is included. The results reveal that the metal and the tertiary butyl groups of the dyes are electron donors, and the tetraphenylporphyrin rings are electron acceptors. The HOMOs of the dyes fall within the (TiO2)60 and Ti38O76 band gaps and support the issue of typical interfacial electron transfer reaction. The resulting potential drop of Mn-TPP-C60 increased by ca. 3.50% under the effect of the tertiary butyl groups. The increase in the potential drop indicates that the tertiary butyl complexes could be a better choice for the strong operation of the molecular rectifiers. The introduction of metal atom and tertiary butyl groups to the tetraphenyl porphyrin moiety leads to a stronger response to the external electric field and induces higher photo-to-current conversion efficiency. This also shifts the absorption in the dyes and makes them potential candidates for harvesting light in the entire visible and near IR region for photovoltaic applications.

Structural and electronic study of iron-based dye sensitizers for solar cells using DFT/TDDFT.

Ruthenium-based molecules have proven their efficiency as photosensitizers in dye-sensitized solar cells. However, due to the high cost and scarcity of this noble metal, in this work we investigated the effects of replacing the ruthenium in photosensitizers with iron because it is less expensive and more abundant. DFT and TD-DFT methods were used to explore the resulting systems. The B3LYP functional was employed to compute the ground-state geometries and the frontier molecular orbitals for four complexes of general formula M(Rbpy)2S2N2C2 (M=Ru or Fe; R=COOH or COOEt). We also used TD-M06 to investigate the electronic properties and to simulate the absorption spectra of these Ru-based and Fe-based complexes. Finally, CPCM was applied to explore the effect of DMF solvent. The HOMOs of these Ru-based and Fe-based molecules were found to have metal d orbital and π(S2C2N2) orbital character, while their LUMOs had π*(R-bpy) orbital character. In addition, values of the light-harvesting efficiency (LHE), open circuit voltage (V oc), and driving force (∆G inject) were calculated for the Ru-based and Fe-based molecules. According to our results, the maximum absorbance, the LHE, V oc, and ∆G inject values for complexes 2 and 4 (Fe-based dyes) are very close to those of complexes 1 and 3 (Ru-based dyes). Thus, our studies indicate that the Ru in photosensitizers can be replaced with the much less expensive metal Fe, as the resulting Fe-based dyes appear to be promising candidates for use in solar cells.

The role of electronic donor moieties in porphyrin dye sensitizers for solar cells: Electronic structures and excitation related properties

The development and synthesis of novel dye sensitizers are important for improving the power conversion efficiency of dye-sensitized solar cells (DSSCs) in terms of the role of dye sensitizers in photon to electricity energy conversion processes. How the different moieties tune the electronic structures and related properties is the fundamental issue in designing dye sensitizers. Here, the geometries, electronic structures, excitation properties, and free energy variations for electron injection (EI) and dye regeneration (DR) of porphyrin dye sensitizers SM315, GY50, FA, and KS, containing bulky bis(2′,4′-bis(hexyloxy)-[1,1′-biphenyl]-4-yl)amine, diarylamino group with two hexyl chains, quinolizinoacridine, and triazatruxene as electron donors, respectively, were investigated. The Q bands absorption spectra of FA and KS exhibit a blue-shift relative to those of SM315 and GY50, resulting from weak conjugation effects. The transition configurations and molecular orbital analysis suggest that the electron donors in these dyes are effective chromophores for photon-induced EI in DSSCs. The torsion angle between the electron-donor and the conjugation-bridge has significant effects on electronic structures, excited states, charge transfer (CT) properties, and free energy variations for EI and DR. The transferred charges and CT distances demonstrate that quinolizinoacridine in FA is the most prominent electron donor moiety among these porphyrin dyes.

Computational study of the impact of regeneration and unwanted recombination reactions of Ru(II) phenanthroline compounds used as sensitizers in dyes sensitized solar cells

The electronic, spectroscopic, regeneration and recombination reactions of four ruthenium(II) phenanthroline complexes with different number and position of the carboxylic acid group were modelled and compared to their reported experimentally obtained efficiencies as sensitizers for dye sensitizer solar cells (DSSCs). The results shows that the excitation of the compounds are associated with shorter CS bonds, lower band gap, and low self-spin electrons on the Ru ion. The interactions of the ruthenium complexes with I− ion indicated that this step is responsible for the electron transfer processes and regeneration while interaction with 2I− ion resulted in the separation of the two I− ion from the ruthenium compounds and their return to the ground states. Thermodynamic properties and the hyperfine values further confirm this observation. The results provided better insights on the regeneration and recombination reactions taken place in these compounds with respect to the discrepancies observed in their efficiencies as sensitizers for DSSCs. The results also show that the interacting energy of the Ru2+ with I− and their associated properties like hyperpolarizability and band gap play significant role in the reported experimental short-circuit photocurrent density (Jsc) and solar-energy conversion efficiency (η).

Photoactive layer based on T-shaped benzimidazole dyes used for solar cell: from photoelectric properties to molecular design

Three benzimidazole-based organic dyes, possessing the same triphenylamine donors and cyanoacrylic acid acceptors with the bithiophene π-bridges combined in different nuclear positions of benzimidazole, were investigated in the utility of dye-sensitizer solar cells. The structure, molecular orbital and energy, absorption spectra and some important parameters (such as light harvesting efficiency (LHE), electron injection driving force, the electron injection time, chemical reactivity parameters, vertical dipole moment as well as interaction models of dye-I2) were obtained according to Newns–Anderson model and DFT calculation. The process and strength of charge transfer and separation were visualized with charge different density and index of spatial extent (S, D and Δq). Current work paid attention to the new T-shaped dyes to reveal the relation between the structure and photoelectric performance. Furthermore, nine dyes (substitution of alkyl chains and π-bridges) have been designed and characterized to screen promising sensitizer candidates with excellent photo-electronic properties.

Structure-property relationship of π-extended boron-dipyrromethene derivatives towards optoelectronic applications

A series of novel boron-dipyrromethenes bearing β-benzo-fused rings, or benzo-BODIPYs, and phenyl, thienyl and bithiophenyl meso-substituents was synthesized, and investigated for their photophysical and electrochemical properties. Results from the UV–visible spectrophotometry revealed that the boron-complexation and the presence of the β-benzo-fused rings significantly increase absorptivity of the molecules in the longer wavelength region. Moreover, according to the observed electrochemical and photophyscial properties of these compounds, the extended conjugation system and the presence of thiophene-based meso-substituents in the target benzo-BODIPYs created great impact on the energy levels of the molecular frontier orbitals, resulting in narrowing of the energy gap of the materials. We have also demonstrated the use of density functional theory calculations to evaluate the performance of these compounds as dye sensitizers in solar cells. While all the molecules studied have their frontier orbitals aligned appropriately with respect to the band gap of TiO2, they are found to differ in their charge injection properties when anchored on TiO2, and even more markedly in electron-hole separation and change in dipole moment upon excitation. Upon combining these criteria using a simple model and the experimental results, the bithiophenyl-substituted benzo-BODIPY was suggested as the optimal candidate.