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.

Designing and theoretical study of benzocarbazole-based D-π-D type small molecules donor for organic solar cells

Seven new molecules (S1-S7) of D-π-D type have been designed for organic photovoltaic applications. The DFT and TD-DFT methods were used to investigate the effect of different central bridge groups on the geometric, optoelectronic, and charge transport properties of the constructed molecules. Among them, S4 and S6 have the lowest energy band gap and a red shift in the absorption spectra, revealing the perfect relationship between the central bridge and the strong electron withdrawal character through extended conjugation. Similarly, S6 explored the lowest reorganization energy (RE) value for electron and hole revealing its enhanced charge transition, also shows better ICT characteristics with its highest NLO properties. Compound S4 showed the smallest value of ΔE_L-L and E_b, and the highest V_oc due to its low HOMO, which improves the photocurrent density of the devices. Thus, the results suggest that bridge modification is a practical strategy to improve the efficiency of OSCs.

Organic Solar Cells: Physical Principle and Recent Advances

Organic solar cells (OSC) based on organic semiconductor materials that convert solar energy into electric energy have been constantly developing at present, and also an effective way to solve the energy crisis and reduce carbon emissions. In the past several decades, efforts have been made to improve the power conversion efficiency (PCE) of OSCs. During this period, a variety of structural and material forms of OSCs have evolved. Commercializing OSCs, extending their service life and exploring their future development are promising but challenging. In this review, we first briefly introduce the development of OSCs and then summarize and analyze the working principle, performance parameters, and structural features of OSCs. Finally, we highlight some breakthrough related to OSCs in detail.

The role of the donor group and electron-accepting substitutions inserted in π-linkers in tuning the optoelectronic properties of D-π-A dye-sensitized solar cells: a DFT/TDDFT study

The design of low-cost and high-efficiency sensitizers is one of the most important factors in the expansion of dye-sensitized solar cells (DSSCs). To obtain effective sensitizer dyes for applications in dye-sensitized solar cells, a series of metal-free organic dyes with the D–π–A–A arrangement and with different donor and acceptor groups have been designed by using computational methodologies based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT). We have designed JK-POZ(1–3) and JK-PTZ(1–3) D–π–A–A organic dyes by modifying the donor and π-linker units of the JK-201 reference dye. Computational calculations of the structural, photochemical properties and electrochemical properties, as well as the key parameters related to the short-circuit current density and open-circuit voltage, including light-harvesting efficiency (LHE), singlet excited state lifetime (τ), reorganization energies (λ_total), electronic injection-free energy (ΔG^inject) and regeneration driving forces (ΔG^reg) of dyes were calculated and analyzed. Moreover, charge transfer parameters, such as the amount of charge transfer (q^CT), the charge transfer distance (D^CT), and dipole moment changes (μ^CT), were investigated. The results show that ΔG^reg, λ_max, λ_total and τ of JK-POZ-3 and JK-PTZ-3 dyes are superior to those of JK-201, indicating that novel JK-POZ-3 and JK-PTZ-3 dyes could be promising candidates for improving the efficiency of the DSSCs devices.

A series of metal-free organic dyes with the D–π–A–A arrangement and with different donor and acceptor groups have been designed theoretically.

Molecular tuning of non-fullerene electron acceptors in organic photovoltaics: a theoretical study

On the basis of the famous A–D–A-type non-fullerene acceptor IT-4F, this work investigates the effects of introducing methyl groups and substituting dicyano with O on optoelectronic properties and photovoltaic performances.

Modulation of Acceptor Position in Organic Sensitizers: The Optimization of Intramolecular and Interfacial Charge Transfer Processes

With respect to cyanoacryclic acid as the traditional acceptor and anchoring group in dye-sensitized solar cells, the introduction of stronger electron-deficient groups has greatly expanded the scope of molecular design and increased their efficiencies for organic dyes. In this contribution, benzothiadiazole (BTD) was selected as a representative acceptor to illustrate the influence of its position on the photophysical properties and corresponding photovoltaic performances. Through the insertion of BTD in different positions of the framework with the same composition units and orders, four sensitizers were designed and synthesized. The structure-property relationship demonstrated the preference of the suitable position of an electron acceptor for optimization of the spectra response and interfacial charge transfer. In our system, dye LI-96 with BTD in the middle of the conjugated bridge showed the broadest spectrum and achieved the best photovoltaic performance (8.25%), which may pave a new way to design or optimize the efficient sensitizers by rational design of the acceptor position.

Theoretical Study on the Use Cyano Acid Derivation as Electron Acceptors in Pelargonidin as Dye Compounds of Sensitized Solar Cells (DSSC)

The theoretical study of the use of cyano acid derivatives as electron acceptor groups in pelargonidin as a dye compound in sensitized solar cells (DSSC) was successfully carried out. Theoretical study was carried out with the purpose to determine the effect modification of the addition of cyanoacrylic benzothiadiazole, cyanoacrylate, cyanovinyl, and cyanocynamic as electron acceptors to the characteristics of pelargonidin as dye DSSC. The effect of modification is based on the parameters of bond length, spectra, molecular electron density, light harvesting efficiency (LHE), (VRP), and HOMO-LUMO energy. The molecular structure created using the Avogadro program, then optimized by DFT/TDDFT method using a base set 6.311G *. Based on the results of research on pelargonidin-benzothiadiazole cyanoacrylate is a better modification when compared with pelargonidin without modification or pelargonidin modified with other cyano acids. This modification is better modification based on parameters molecular electron density, HOMO-LUMO energy, (VRP), bond lengths, and spectra. Pelargonidin-benzothiadiazole cyanoacrylic electron density in LUMO conditions centred in benzothiadiazole cyanoacrylic, HOMO and LUMO energy of dye is -4.97856 eV & -2,56731 eV, VRP value 0.439, bond lengths 1.936 Å, and spectra at wavelength 393.14 nm & 377.09 nm. Based on the light harvesting efficiency (LHE), pelargonidin without modification is the best modification with an LHE value 0.820.

Theoretical investigation of auxiliary electronic acceptors in modifying D-D-π-A sensitizers for dye-sensitized solar cells

In light of the performance of the SD2 pigments in DSSC, in order to expand the absorption spectral scope, decrease the energy difference between the highest occupied and the lowest unoccupied molecular orbitals, with SD2 dye molecular electron donor and electron acceptor as the fundamental framework, the indole fragment and thiophene derivative in the prototype dye molecule were replaced by the two π-bridges (labeled PA, PB, respectively) and the four auxiliary electron acceptors (labeled A1, A2, A3, A4, respectively). For the sake of characterizing dye molecules as thoroughly as possible in DSSC, the frontier orbital energy levels, ultraviolet absorption spectra, natural bond orbital analysis, intramolecular charge transfer, charge and hole reorganization energies, parameters influencing the short-circuit current density and the open-circuit photovoltage for these eight individual dye molecules are carried out to try to fully characterize the properties of these dye molecules. According to these computational results of physical quantities and based on the performance of these dye molecules in the above aspects, in this paper, six free molecular models were picked out to combine with titanium dioxide cluster to calculate their geometrical structures, frontier orbital distributions, electron excitation energies, ultraviolet absorption spectra and the composition of the electronic transitions in chloroform solvent with polarizable continuum model. The results of these calculations show that the PA-A2 and PB-A4 dye molecule has better properties in electron transfer and spectral absorption range before and after the adsorption on the titanium dioxide.

Photoactuated Properties of Acetylene-Congeners Non-Metallic Dyes and Molecular Design for Solar Cells

This paper theoretically simulated (using DFT and TD-DFT in N,N-dimethylformamide (DMF) solvent) the photodynamic properties of three non-metallic dye molecules with D-π-A₁-π-A₂ structure. The total photoelectric conversion efficiency (PCE) could be evaluated by the following parameters: the geometric structures, the electronic structures, and the absorption spectra, the analyses of charge difference density (CDD) and natural bond orbitals (NBO), the analyses of ionization potential (IP) and electron affinity (EA) from electronic contribution capacity, the reorganization energies (λh, λe, and λtotal), and the chemical reaction parameter (h, ω, ω−, and ω+) for intramolecular charge transfer (ICT) processing, the excited lifetime (τ) and the vertical dipole moment (μnormol). The ∆Ginject, the ∆Gdyeregen, the light harvesting efficiencies (LHE) and the excited lifetime (τ) were used to explain experimental JSC. The experimental trend of VOC was explained by the calculation of ∆ECB and μnormol. Moreover, the 15 dyes were designed by adding the electron-donor groups (–OH, –NH₂, and –OCH₃) and the electron-acceptor groups (–CF₃, –F, and –CN) to the LS-387 molecular skeleton, which improved electronic contribution, intramolecular charge transfer (ICT), and optoelectronic performance.

Structure and Photoelectrical Properties of Natural Photoactive Dyes for Solar Cells

A series of natural photoactive dyes, named as D1–D6 were successfully extracted from six kinds of plant leaves for solar cells. The photoelectrical properties of dyes were measured via UV-Vis absorption spectra, cyclic voltammetry as well as photovoltaic measurement. To theoretically reveal the experimental phenomena, the chlorophyll was selected as the reference dye, where the ground and excited state properties of chlorophyll were calculated via density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The experimental results show that the absorption peaks of those dyes are mainly distributed in the visible light regions of 400–420 nm and 650–700 nm, which are consistent with the absorption spectrum of chlorophyll. The photoelectrical conversion efficiencies of the solar cells sensitized by the six kinds of natural dyes are in the order of D1 > D4 > D2 > D5 > D6 > D3. The dye D1 performance exhibits the highest photoelectrical conversion efficiency of 1.08% among the investigated six natural dyes, with an open circuit voltage of 0.58 V, a short-circuit current density of 2.64 mA cm−2 and a fill factor of 0.70.

Physical Insight on Mechanism of Photoinduced Charge Transfer in Multipolar Photoactive Molecules

Two series of novel dyes were designed based on the multipolar structures of the red dye D35 and blue dye DB, by introducing the furan (F), benzene ring (B) and benzo[c]thiophene (BT) groups into the conjugated bridge of D35 in proper order and adjusting the position of diketopyrrolopyrrole(DPP) unit and the incorporation of fluorine in the conjugated bridge of DB, respectively. We performed the quantum chemistry calculation to investigate the ground state and excited properties in a direct correlation with the spectra properties and abilities of losing or accepting electron for the original and designed molecules. Furthermore, the absorption spectra characteristics in consideration of the aggregation of dyes on the TiO₂ layer and intermolecular charge transfer rate of the dimers were calculated. The obtained results indicate that the larger intermolecular charge transfer rate leads to the poor photoelectrical properties of the dyes, and the designed dyes D35-3 and DB-2 would exhibit the best photoelectrical properties among the investigated dyes due to their lower energy gaps, widened absorption spectra and prominent charge transfer properties.

Tunable ESIPT reaction and antioxidant activities of 3-hydroxyflavone and its derivatives by altering atomic electronegativity

3-HTF easiest to carry out ESIPT reaction would exhibit the highest efficient antioxidant activity among the three compounds.

Double-anchoring organic dyes for dye-sensitized solar cells: the opto-electronic property and performance

A series of A–D–π–D–A multi-anchoring organic dyes (MA-201–MA-206) with different core spacers was designed to investigate optoelectronic properties and to develop utility for solar cells.