Impact of internal (donor/acceptor) moieties and π-spacer in triphenylamine-based dyes for DSSCs

Unveiling the potential of TPA-based molecules to tune the optoelectronic properties and enhance the efficiency of dye-sensitized solar cells

CONTEXT

The world's energy and environmental requirements are changing due to rapid population growth and industrial growth, and solar cells can be used to meet these demands. Dye-sensitized solar cells (DSSCs) are solar cells in which energy conversion occurs via a process similar to photosynthesis in plants. DSSC development is still in its infancy. DSSCs can operate under cloudy conditions and indirect sunlight and have attracted considerable attention due to their low cost and high efficiency. We designed two metal-free TPA-based dyes (Dye2 and Dye3) based on the reference dye Mg207 (Dye1) by increasing the donor strength of the molecule, as such dyes have shown enhanced efficiency in DSSCs. Moreover, the triphenylamine (TPA) moiety has been demonstrated to be a good donor that prevents charge recombination. Intramolecular charge transfer (ICT) from the donor to acceptor moiety was found in the sensitizers, and electrons were promoted to the conduction band (CB) of the TiO2 semiconductor. The negative binding energy of the dye@TiO2 clusters indicated that dye adsorption on the semiconductor surface was stable. The double donor increased the electron injection and electronic coupling constants in Dye2 and Dye3, indicating that these newly designed dyes have superior charge injection capacity. Accordingly, the efficiencies of DSSCs with Dye2 and Dye3 were 9.77% and 9.62%, respectively, and substitution with the TPA unit at the -R1 and -R2 positions in Dye1 resulted in better power conversion compared to the parent compound (9.09%). Increased donor strength improved photovoltaic performance by increasing current density and light-harvesting efficiency. This is a good molecular design approach for preparing targeted donor- π -acceptor (D- π -A) organic dyes with high DSSC efficiency.

METHODS

To predict the charge transport and optoelectronic characteristics of the TPA dyes, quantum chemical calculations were carried out using Gaussian16. The ground-state (S0) optimized geometries of the sensitizers were computed by utilizing DFT at the B3LYP/6-31G** level. The absorption spectra ( λ max) were computed by employing TD-DFT with various functionals (B3LYP, PBE1PBE, CAM-B3LYP, and BHandHLYP) in the gas and solvent (DCM) phases. Among the studied functionals, BHandHLYP was found to be best at successfully reproducing the experimental data. Thus, the absorption spectra of the newly designed dyes and dye@TiO2 were calculated at the BHandHLYP/6-31G** level. The dye@TiO2 cluster optimizations were carried out at the B3LYP/6-31G**(LANL2DZ) level.

DFT and TD-DFT Studies of D-π-A Organic Dye Molecules with Different Spacers for highly Efficient Reliable Dye Sensitized Solar Cells

This study focuses on six D-π-A systems, utilizing diverse π-spacers as bridges. Comprehensive analysis through Density Functional Theory (DFT) and Time-dependent Functional Theory (TD-DFT) methods at B3LYP using 6-31G (d.p) basis set explores geometrical, electrical, optical, photovoltaic, and absorption properties. EHOMO, ELUMO, and energy gap (Egap), for all of these dyes have been determined and discussed using ground state optimization. TD-DFT calculates optical properties, unveiling enhanced excitation energies and HOMO-LUMO energy levels, indicative of improved electron injection and dye regeneration processes. Examination of energy gap, open-circuit voltage (VOC), free energy change (ΔGinject), light harvesting efficiency (LHE), and absorption spectra reveals D4 dye's lower Egap and robust absorption in the visible spectrum. Molecular tailoring emerges as a promising technique for optimizing D-π-A sensitizer design, offering potential advancements in DSSCs applications.

Molecular engineering of Pyran‐fused acceptor–donor–acceptor‐type non‐fullerene acceptors for highly efficient organic solar cells—A density functional theory approach

The end‐capped modification proves that it is an excellent attempt to improve the solar cells performances. Therefore, nowadays, many researchers are working to design new molecules for potential use in organic photovoltaics. Herein, we have modified new molecules (SA1–SA5) from the reference (R) for fullerene‐free solar cells. These novel molecules have lower excitation energy levels that make the easier excitation in the excited state. Additionally, SA1 to SA5 molecules exhibit excellent charge mobility due to the modification of an efficient core units. Geometric and physiochemical investigations indicate that the modeled molecules are beneficial for efficient organic solar cells. The estimation of frontier molecular orbitals analysis, reorganizational energy, photovoltaic characteristics, and charge transmission calculations was done using density functional theory calculations with B3LYP/6‐31G (d, p) basis set. Among all designed molecules, SA3 has emerged as the preferred choice because of its outstanding photovoltaic characteristics, which include a minimal bandgap of 2.03 eV and reorganization energy of electron and holes of 0.0095 and 0.0077 eV, correspondingly. The designed materials (SA1–SA5) displayed a high λ max values, that is, 693.54 nm (in gas) and 679.63 nm (in chloroform). This theoretical framework suggests that the required photovoltaic properties may be efficiently obtained by remodeling the new molecules.

The impact of aromatic π-spacers and internal acceptors in triphenylamine dyes for DSSCs: A DFT approach

In present work, the influence of internal acceptors and π-spacers on optoelectronic properties for dye-sensitized solar cells (DSSCs) is investigated. The dyes consist of various internal acceptors (A), a triphenylamine donor and π-spacers combined with cyanoacrylic acid acceptor. Density functional theory (DFT) was employed to inspect the dye geometries, charge transport characteristics and electronic excitations. The frontier molecular orbitals (FMOs), highest occupied molecular orbital, lowest unoccupied molecular orbital and HOMO-LUMO energy gap are assisted in the determination of suitable energy levels for electron transfer, electron injection and regeneration of dye. The required photovoltaic parameters like J_SC, ΔG_reg, ΔG_inj, LHE and other associated parameters are presented. The results demonstrate that altering the π-bridge and adding an internal acceptor to the D-π-A scaffold changes the photovoltaic properties and absorption energies. Therefore, the key objective of the current effort is to launch a theoretical groundwork for suitable operational alterations and scheme in creating successful DSSCs.

Optoelectronic design and charge transport properties of Benzodifuran (BDF) isomers for organic electronic devices: DFT/TD-DFT insights

The primary goal of this work is to provide a comprehensive analysis of the charge transport and optoelectronic characteristics of all the isomers of benzodifuran (BDF) for organic electronic devices in order to suggest qualified materials/candidates for organic photovoltaic devices. Density functional theory (DFT) calculations were performed for all possible isomers of BDF and results are compared with corresponding experimental known isomers. Time Dependent-Density Functional Theory (TD-DFT) is used for the calculation of the absorption and HOMO-LUMO energy levels. To characterize the electronic charge transport state in these isomers, the ionization potentials (IP), reorganization energies (hole and electron), and electron affinities (EA) of all the isomers are investigated. Comparatively, all the BDF isomers are having low electron and hole reorganization energies and hence they can be used in the organic electronic material fabrication.