Designed complexes combining brazilein and brazilin with betanidin for dye-sensitized solar cell application: DFT and TD-DFT study.

Dye-sensitized solar cells (DSSCs) are promising third-generation photovoltaic cell technology owing to their easy fabrication, flexibility and better performance under diffuse light conditions. Natural pigment sensitizers are abundantly available and environmentally friendliness. However, narrow absorption spectra of natural pigments result in low efficiencies of the DSSCs. Therefore, combining two or more pigments with complementary absorption spectra is considered an appropriate method to broaden the absorption band and boost efficiency. This study reports three complex molecules: brazilin-betanidin-oxane (Braz-Bd-oxane), brazilin-betanidin-ether (Braz-Bd-ether) and brazilein-betanidin-ether (Braze-Bd-ether), obtained from the etherification and bi-etherification reactions of brazilin dye and brazilein dye with betanidin dye. The equilibrium geometrical structure properties, frontier molecular orbital, electrostatic surface potential, reorganization energy, chemical reactivities, and non-linear optical properties of the studied dyes were investigated using density functional theory (DFT)/B3LYP methods, with 6-31+G(d,p) basis sets and LANL2DZ for light atom and heavy atoms respectively. The optical-electronic properties were calculated using TD-DFT/B3LYP/6-31+G(d,p) for isolated dye and TD-DFT/CAM-B3LYP/6-31G(d,p)/LANL2DZ for dyes@(TiO2)9H4. The results reveal that spectra for Braz-Bd-oxane and Braze-Bd-ether complexes red-shifted compared to the individually selected dyes. The simulated absorption spectra of the adsorbed dyes on (TiO2)9H4 are red-shifted compared to the free dye. Moreover, Braz-Bd-oxane and Braz-Bd-ether exhibit better charge transfer and photovoltaic properties than the selected natural dyes forming these complexes. Based on the dyes' optoelectronic properties and photovoltaic properties, the designed molecules Braz-Bd-oxane and Braze-Bd-ether are considered better candidates to be used as photosensitizers in dye solar cells.

Optical and electronic properties enhancement via chalcogenides: promising materials for DSSC applications.

CONTEXT: Comparatively, metal-free sensitizers featuring the chalcogen family receive less attention despite known electronic properties for metal-chalcogenide materials. This work reports an array of optoelectronic properties using quantum chemical methods. Observed red-shifted bands within the UV/Vis to NIR regions with absorption maxima > 500 nm were consistent with increasing chalcogenide size. There is a monotonic down-shift in the LUMO and ESOP energy consistent with O 2p, S 3p, Se 4p, to Te 5p atomic orbital energies. Excited-state lifetime and charge injection free energies follow the decreasing order of chalcogenide electronegativity. Adsorption energies of dyes on TiO2 anatase (101) range between - 0.08 and - 0.77 eV. Based on evaluated properties, selenium- and tellurium-based materials show potential use in DSSCs and futuristic device applications. Therefore, this work motivates continued investigation of the chalcogenide sensitizers and their application. METHODS: The geometry optimization was performed at B3LYP/6-31 + G(d,p) and B3LYP/LANL2DZ level of theory for lighter and heavier atoms, respectively, using Gaussian 09. The equilibrium geometries were confirmed by the absence of imaginary frequencies. Electronic spectra were obtained at CAM-B3LYP/6-31G + (d,p)/LANL2DZ level of theory. Adsorption energies for dyes on a 4 × 5 supercell TiO2 anatase (101) were obtained using VASP. The dye-TiO2 optimizations were employed using GGA and PBE with the PAW pseudo-potentials. The energy cutoff was set at 400 eV and convergence threshold for self-consistent iteration was set to 10-4, and van der Waals were accounted using DFT-D3 model and on-site Coulomb repulsion potential set at 8.5 eV for Ti.

Performance enhancement of catechin-graphene quantum dot nanocomposites functionalized with carboxyl and doped/decorated with boron towards dye-sensitized solar cell applications: DFT and TD-DFT calculations.

A photosensitizer plays a vital role in adjusting the optical and electrochemical properties that affect the performance of dye-sensitized solar cells (DSSCs). Therefore, it should meet critical requirements for efficient operation of DSSCs. This study proposes catechin, a natural compound, as a photosensitizer and modifies its properties through hybridization with graphene quantum dots (GQDs). Density functional theory (DFT) and time-dependent DFT methods were used to investigate the geometrical, optical, and electronic properties. Twelve nanocomposites of catechin attached to carboxylated/uncarboxylated GQD were designed. The GQD was further doped with central/terminal boron atom or decorated with boron groups (organo-borane, borinic, and boronic groups). The available experimental data of parent catechin was used to validate the elected functional and basis set. Through hybridization, the energy gap of catechin was significantly narrowed by 50.66-61.48%. Therefore, its absorption was shifted from the UV to the visible region which matches the solar spectrum. Also, increasing the absorption intensity led to high light-harvesting efficiency close to unity that can increase current generation. The energy levels of designed dye nanocomposites are appropriately aligned with the conduction band and redox potential, indicating the feasibility of electron injection and regeneration. The observed properties confirm that the reported materials exhibit characteristics of interest thus they could be promising candidates for applications in DSSCs.

Prediction of Power Conversion Efficiencies of Diphenylthienylamine-Based Dyes Adsorbed on the Titanium Dioxide Nanotube.

The power conversion efficiency (η) is the most important key to determine the efficiency of dye-sensitized solar cell (DSSC) devices. However, the calculation of η theoretically is a challenging issue since it depends on a large number of experimental and theoretical parameters with extensive related data. In this work, η was successfully predicted using the improved normal model with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) for eight diphenylthienylamine-based (DP-based) dyes with various π-bridge adsorbed on titanium dioxide. The titanium dioxide is represented by a nanotube surface (TiO2NT); this surface is rarely investigated in the literature. The π-linker consists of five (DP1)- or six (DP2)-membered rings and contains none to three nitrogen atoms (D0-D3). The reliability of the estimated values was confirmed by the excellent agreement with those available for the two experimentally tested ones (DP2-D0 and DP2-D2). The deviations between the experimental and estimated values were in the ranges of 0.03 to 0.06 mA cm-2, 0.05 to 0.3 mV, and 0.37 to 0.18% for short-circuits current density (J sc), open-circuit voltage (V oc), power conversion efficiency (%η), respectively. More importantly, the results revealed that using pyridine (DP2-D1), pyrimidine (DP2-D2), and 1,2,4-triazine (DP2-D3) improves the power conversion efficiencies in the range of 6.03 to 6.90%. However, the cyclopenta-1,3-diene (DP1-D0) shows superior performance with a predicted η value that reaches 9.55%.

Single- and co-sensitization of triphenylamine-based and asymmetrical squaraine dyes on the anatase (001) surface for DSSC applications: Periodic DFT calculations.

Dye aggregation causes poor performance of dye-sensitized solar cell (DSSC) applications through faster charge recombination of the photosensitizer with electrolyte. Triphenylamine (TBA)-based dyes feature a higher molar absorption coefficient and broadened wavelength but cannot absorb sunlight in the near-infrared (NIR) region. In contrast, the squaraine (SQ) photosensitizer, which is also called an NIR photosensitizer, has a maximum wavelength in the NIR region with high intensity. However, SQ dye suffers from dye aggregation due to its planar structure. The use of a co-sensitizer is one well-tested way to increase the power conversion efficiency (η) of solar cells by reducing dye aggregation and charge recombination. Using density functional theory (DFT) and time-dependent DFT (TDDFT), this work explains from a theoretical perspective the higher η values of the TZC1 and TZC2 dyes compared to that of asymmetric the SQ sensitizer (YR6) as free dyes. The electronic properties, reorganization energies, absorption and emission spectra, ICT parameters, and photovoltage parameters of the TZC1, TZC2, and YR6 dyes were computed using the M06/6-31G(d,p) level of theory in the gas phase and CH2Cl2 solvent (CPCM method). Additionally, the mono- and co-adsorption processes of TZC-based sensitizers with YR6 on the anatase (001) surface were investigated using periodic DFT calculations with the PBE + U/PAW method and the dispersion correction of the Grimme method D3. The results reveal that the use of the co-sensitized led to significant stabilization of the formed complexes by at least 1.21 eV, the panchromatic effect on the absorption spectra, and an increase in the light-harvesting ability in the NIR region, which improves the performance of DSSCs.

Effects of heteroatoms in π-conjugated linkers on the optical and electronic properties of modified triphenylamine based dyes: towards DSSCs' applications.

Optoelectronic properties of triphenylamine dyes arising from the embedded five-membered π-linkers C4H4X (X = O, NH, S, Se, Te) and varying anchoring groups, cyanoacrylic acid and hydantoin, in D-π-π-A model are examined. The reported properties for both, isolated dyes and dye@TiO2 complexes, are realized through density functional theory (DFT) and time-dependent DFT. The study reveals that chalcogen doping (X = S, Se, Te) enhances absorption and fluorescent emission spectra in the visible and NIR regions. The adsorption of the dyes on the TiO2 cluster has been simulated. Alteration of the UV-Vis spectra and electron density redistribution for the complexes from individual dyes are examined and analyzed. The binding energies relate to the nature of the heteroatoms X; the complexes dye@TiO2 with heavier heteroatoms Se and Te demonstrate stronger binding. Graphical abstract.