Molecular Engineering and Theoretical Investigation of Novel Metal-Free Organic Chromophores for Dye-Sensitized Solar Cells

Molecular Design and DFT Analysis of High-performance Dyes Based on Pyrene with Different Donor Parts and Their Optoelectronic Applications

The performance and efficacy of dyes, which are crucial photon-harvesting components in dye-sensitized solar cells (DSSCs), must be meticulously analysed at the molecular level. This research focuses on a theoretical investigation of dye characteristics rather than the synthesis of novel compounds. Using Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT), we have analysed six D-π-A structure dyes designed with pyrene as the π-bridge and various functional groups as donors. Our study examines their geometrical, electronic, optical, electronic localization, and electrochemical properties. The findings reveal that these theoretically designed D-π-A dyes show significant improvements in light-harvesting efficiency, open-circuit photovoltage, electron injection efficiency, and overall photovoltaic performance. The analysis indicates effective electron injection from each dye into the conduction band of TiO2, followed by efficient regeneration and enhanced intra- and intermolecular charge transfer properties. The incorporation of pyrene as a π-bridge and the use of different functional groups as donors are crucial for facilitating electron transfer from the donor to the acceptor region. Among the dyes studied, the D-π-D modified dye demonstrates superior theoretical performance, attributed to its higher energy levels of the lowest unoccupied molecular orbital and greater oscillator strengths for excited states. This results in improved intramolecular electron transfer and electron injection into the conduction band of TiO2, followed by effective regeneration. Overall, our study highlights the potential of these theoretically modeled dyes as highly promising sensitizers for DSSCs, due to their exceptional optical and electronic properties and impressive photovoltaic parameters. These findings position these molecular structures as strong candidates for future applications in organic DSSCs.

Experimental and Computational studies on Intramolecular charge transfer, Terahertz and Two photon absorption of 3-[(4-Nitrophenyl Azo)]-9H-Carbazole-9-Ethanol (NPACE) from their Vibrational spectra for Optical limiting and NLO applications

Non-linear optical (NLO) features of 3-[(4-Nitrophenyl Azo)]-9H-Carbazole-9-Ethanol (NPACE) chromophore were investigated by FT-IR, FT-Raman, and UV-visible spectra aided by Density Functional Theory (DFT) using the B3LYP/6-311++G(d,p) basis set of Gaussian 16 W package. It is observed from the DFT calculation that the slight increase in the endocyclic angle of C13 -C14 -C15 and the reduction in exocyclic angle of N40 -N39 -C14 and C15 -C14 -N39 ascertained by experimental XRD values indicating the intramolecular charge-transfer interaction between the carbazole and nitrophenyl group through the diazo bridge. The vibrational contribution to the linear electro-optic effect is 15% of the total hyperpolarizability being calculated at B3LYP/6-311++G (d, p) for the NPACE molecule. It is also observed that the 8a, 19a, and 19b modes of the carbazole ring and the 8a, 8b, and 19b modes of the phenyl ring are found to be simultaneously and intensely active in IR and Raman spectra explaining the charge transfer interactions throughout the molecule. The low value of the HOMO- LUMO energy gap (2.5843 eV) and the deviation between the measured absorption wavelength (3.36 eV) from the computed (3.87 eV), both these facts substantiate the intramolecular charge transfer. The polarizability and first-order hyperpolarizability were calculated as 6.48 × 10-24 and 3.8 × 10-29 esu, respectively. The second harmonic generation (SHG) measurement experiment of NPACE was carried out using the powder method. The SHG efficiency is measured in comparison with the urea standard. The calculated torsional mode at 20 cm-1 is in excellent quantitative agreement with the experimentally determined terahertz absorption peak. The two-photon absorption coefficient of NPACE was estimated to be 0.9 × 10-11 mW-1, which is mainly due to the D-π-A type of molecular structure, and the optical limiting threshold for NPACE was estimated to be 1.52 × 1013 Wm-2 enabling this material as a potential candidate for optical limiting applications.

The molecular engineering, synthesis and photovoltaic studies of a novel highly efficient Ru(ii) complex incorporating a bulky TPA ancillary ligand for DSSCs: donor versus π-spacer effects

The IA-7 complex was applied in DSSCs.

Simple thiophene-bridged D-π-A type chromophores for DSSCs: a comprehensive study of their sensitization and co-sensitization properties

Herein, we report the design and synthesis of four new thiophene-bridged D-π-A configured organic dyes T1-4 comprising different donors, π-spacers and anchoring units, as potential sensitizers and co-sensitizers for DSSCs. The current work also highlights their structural, photophysical, thermal, electrochemical, theoretical, and photoelectrochemical studies, including evaluation of their structure-property relationships. The optical results revealed that the dyes T1-4 display λabs and λemi in the range of 402-461 nm and 556-575 nm, respectively, with a bandgap in the order of 2.31-2.58 eV. Furthermore, the results showed that the dyes possess all the pre-requisites to act as sensitizers/co-sensitizers. Among the tested dyes, the device based on sensitizer T2 achieved the highest PCE compared to the other three dyes, under the standard conditions. Furthermore, their co-sensitized devices were fabricated by co-adsorbing them with the well-known Ru-based MH-12 sensitizer and interestingly the co-sensitizer T3 carrying an alkoxy group and a barbituric acid anchor displayed the highest PCE of 8.79%, which is much higher than that of MH-12 alone (8.18%). Conclusively, the study furnishes a deeper understanding of the intricacies involved in the structural modification of sensitizers/co-sensitizers in achieving an enhanced performance of the devices.

[1,2,5]Thiadiazolo[3,4-d]Pyridazine as an Internal Acceptor in the D-A-π-A Organic Sensitizers for Dye-Sensitized Solar Cells

Four new D-A-π-A metal-free organic sensitizers for dye-sensitized solar cells (DSSCs), with [1,2,5]thiadiazolo[3,4-d]pyridazine as internal acceptor, thiophene unit as π-spacer and cyanoacrylate as anchoring electron acceptor, have been synthesized. The donor moiety was introduced into [1,2,5]thiadiazolo[3,4-d]pyridazine by nucleophilic aromatic substitution and Suzuki cross-coupling reactions, allowing design of D-A-π-A sensitizers with the donor attached to the internal heterocyclic acceptor not only by the carbon atom, as it is in a majority of DSSCs, but by the nitrogen atom also. Although low values of power conversion efficiency (PCE) were found, a few important consequences were identified: (i) poor PCE data can be attributed to high electron deficiency of the internal [1,2,5]thiadiazolo[3,4-d]pyridazine acceptor due to lower light harvesting by the dye; (ii) the manner in which the donor was attached to the internal acceptor (by carbon or nitrogen) did not play an essential role in the photovoltaic properties of the dyes; (iii) dyes based on the novel donor 2,3,4,4a,9,9a-hexahydro-1H-1,4-methanocarbazolyl and 9-(p-tolyl)-2,3,4,4a,9,9a-hexahydro-1H- carbazole moieties showed similar photovoltaic properties to dyes based on the well-known 4-(p-tolyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indolyl building block, which opens the door for further optimization potential of new dye families.

Simple diphenylamine based D–π–A type sensitizers/co-sensitizers for DSSCs: a comprehensive study on the impact of anchoring groups

Three new diphenylamine based metal-free dyes were designed and developed as efficient sensitizers as well as co-sensitizers along with N3 in DSSCs. Their detailed photophysical, electrochemical, theoretical and photovoltaic properties have been explored.

Co-sensitization of Ru(ii) complex with terthiophene-based D–π–π–A metal-free organic dyes for highly efficient dye-sensitized solar cells: influence of anchoring group on molecular geometry and photovoltaic performance

In this work, we studied the photovoltaic performance of two novel metal-free organic dyes carrying the same donor but with different anchoring moieties.

Optical and Photophysical Investigation of (2E)-1-(2,5-Dimethylfuran-3-Yl)-3-(9-Ethyl-9H-Carbazol-3-Yl)Prop-2-en-1-One (DEPO) by Spectrofluorometer in Organized Medium

(2E)-1-(2,5-dimethylfuran-3-yl)-3-(9-ethyl-9H-carbazol-3-yl)prop-2-en-1-one (DEPO) was prepared by the reaction of 9-ethyl-9H-carbazole-3-carbaldehyde with 1-(2,5-dimethylfuran-3-yl)ethanone under microwave irradiation. The structure of DEPO was established experimentally by EI-MS, FT-IR, ¹H and ¹³C NMR spectral studies. Electronic absorption and emission spectra of DEPO were studied in different solvents on the basis of polarities, and the obtain data were used to determine the solvatochromic properties such as extinction coefficient, oscillator strength, transition dipole moment, stokes shift, fluorescence quantum yield and photochemical quantum yield. Photochemical quantum yield (Φ _c ) of DEPO dye was determined in different solvent. The dye comparatively photostable in DMSO but undergoes photodecomposition in chloro methane solvents. The DEPO dye may be use as probe or quencher to determine critical micelle concentration (CMC) of cetyltri methyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS).

Optical properties and fluorescence quenching of carbazole containing (D–π–A) push–pull chromophores by silver nanoparticles: a detailed insight via an experimental and theoretical approach

(4Z)-4-[(9-Ethyl-9H-carbazol-3-yl)methylidene]-2-phenyl-1,3-oxazol-5(4H)-one (ECPO) was prepared by the one-pot multi-component reaction of 9-ethyl-9H-carbazole-3-carbaldehyde, hippuric acid, anhydrous sodium acetate and acetic anhydride under microwave irradiation.

New indole based co-sensitizers for dye sensitized solar cells exceeding 10% efficiency

In this work, we report the molecular engineering and synthesis of three novel indole co-sensitizers DBA-3, DBA-4 and DBA-5 with D–D–A (donor–donor–acceptor) architecture.