Design of sensitizer with suitable frontier molecular orbital via substitution on starburst triphenylamine derivative

Herein, a series of organic molecules were designed through locating different substituents on the compound (WD8-c-1) to develop their performances used as the sensitizers in the field of dye-sensitized solar cells. The geometry and relevant electronic properties of WD8-c-1 and its derivatives were simulated at the B3LYP/6-31G(d,p) level. The absorption spectra were calculated using the TD-PBE0/6-31+G(d,p) method. These calculated results show that the type and position of the substituents strongly affected the distributions of frontier molecular orbitals and the energy gaps for the WD8-c-1-derived molecules. The reorganization energies results reveal that their hole charge transfer rates are higher than that of the representative hole transport material. Moreover, the mobility of the representative WD8-c-1 derivative also has been simulated. The starburst triphenylamine with suitable substituent has the more suitable FMO energy to match those of TiO₂, broad absorption region, smaller reorganization energies, and high hole mobility.

Density functional theory design of double donor dyes and electron transfer on dye/TiO2(101) composite systems for dye-sensitized solar cells

In this work, we designed a series of double donor organic dyes, named ME101-ME106, based on experimentally synthesized dye WD8, and further investigated their electronic structure, the stability of the dye/TiO₂ (101) systems, density of states (DOS) and absorption spectra using density functional theory (DFT) and time-dependent DFT (TDDFT). The molar extinction coefficients of all designed dyes are higher than WD8. It's fascinating that ME106 exhibits a smallest energy gap and 75 nm redshifts compared to WD8. The results of calculations reveal that ME101-ME106/TiO₂(101) surfaces are more stable than WD8, double donor dyes have sufficient electron injection driving force and have very strong transfer electron ability. It is expected that the design of double donors can provide a new understanding and guidance for the investigation of high efficiency dye-sensitized devices.

Unsymmetrical β-functionalized ‘push–pull’ porphyrins: synthesis and photophysical, electrochemical and nonlinear optical properties

A new family of unsymmetrical β-TPA appended ‘push–pull’ porphyrins has been synthesized in good yield for the first time. They exhibited red shifted broad absorption spectral features with high dipole moments and tunable redox properties.

Ru(II) porphyrins as sensitizers for DSSCs: Axial vs. peripheral carboxylate anchoring group

In this study, two porphyrin chromophores metallated with ruthenium, RuTBP and RuTBPPy, were prepared and studied as sensitizers in dye-sensitized solar cells (DSSCs). The difference between the two dyes is the position (axial vs. peripheral) of the carboxylic anchoring group. This work examines the impact of this variation towards the optical, electrochemical and photovoltaic performance of DSSCs. The thorough photophysical and photovoltaic measurements indicated that the peripherally substituted sensitizer (RuTBP) presented higher photovoltaic performance compared to RuTBPPy. More specifically, DSSCs sensitized with RuTBP and RuTBPPy displayed an overall power conversion efficiency (PCE) of 5.12% and 4.08%, respectively. The higher PCE value of the DSSC sensitized with RuTBP is mainly attributed to the enhancement of [Formula: see text] and FF values. These factors were enhanced due to the efficient dye regeneration process, the suppression of back-charge recombination reactions and the longer electron lifetimes as evidenced from the electrochemical impedance spectra.

Effect of furan π-spacer and triethylene oxide methyl ether substituents on performance of phenothiazine sensitizers in dye-sensitized solar cells

Synthesis and characterization of three phenothiazine dyes inspired by literature dye EO3 improving absorption properties and photovoltaic performance in DSSCs.

Synthesis by a Cost-Effective Method and Electroluminescence of a Novel Efficient Yellowish-Green Thermally Activated Delayed Fluorescent Molecule

A new thermally activated delayed fluorescent molecule, TRZ 3(Ph-PTZ), containing three phenothiazines as donor units and a 2,4,6-triphenyl-1,3,5-triazine as the acceptor unit was synthesized using a simple cost-effective method based on a cobalt catalyzed cross-coupling. This compound was tested in organic light-emitting diodes and was found to show superior yellowish-green electroluminescence performance with a maximum external quantum efficiency of 17.4% and a maximum luminance value of 7430 cd/m².

S,N-Heteroacene-Based Copolymers for Highly Efficient Organic Field Effect Transistors and Organic Solar Cells: Critical Impact of Aromatic Subunits in the Ladder π-System

Three novel donor-acceptor alternating polymers containing ladder-type pentacyclic heteroacenes (PBo, PBi, and PT) are synthesized, characterized, and further applied to organic field effect transistors (OFETs) and polymer solar cells. Significant aspects of quinoidal characters, electrochemical properties, optical absorption, frontier orbitals, backbone coplanarity, molecular orientation, charge carrier mobilities, morphology discrepancies, and the corresponding device performances are notably different with various heteroarenes. PT exhibits a stronger quinoidal mesomeric structure, linear and coplanar conformation, smooth surface morphology, and better bimodal crystalline structures, which is beneficial to extend the π-conjugation and promotes charge transport via 3-D transport pathways and in consequence improves overall device performances. Organic photovoltaics based on the PT polymer achieve a power conversion efficiency of 6.04% along with a high short-circuit current density (J_SC) of 14.68 mA cm^-2, and a high hole mobility of 0.1 cm² V^-1 s^-1 is fulfilled in an OFET, which is superior to those of its counterparts, PBi and PBo.

Facile synthesis of triphenylamine and phenothiazine-based Schiff bases for aggregation-induced enhanced emission, white light generation, and highly selective and sensitive copper(ii) sensing

Facile synthesis of triphenylamine and phenothiazine based Schiff bases for multiple applicability, viz., in AIEE, WLE and Cu²⁺ sensing.

Iodine induced 1-D lamellar self assembly in organic ionic crystals for solid state dye sensitized solar cells

A novel saturated heterocyclic organic ionic crystal, piperidinium iodide (PiHI), is synthesized by a facile route and applied as a solid electrolyte in Dye Sensitized Solar Cells (ss-DSSCs). Upon addition of a small quantity of iodine, PiHI self-assembles into a 1D lamellar micro crystalline structure that shows anisotropic conductivity. The two-component PiHI was characterized by using electrochemical impedance spectroscopy, cyclic voltammetry, steady state voltammetry, FT-IR, and Raman spectroscopy. Wide angle X-ray diffraction (XRD) measurement confirms the presence of long range 1D lamellar channels that pave the way for the diffusion of the redox couple I^-/I₃^- and exhibit high anisotropic conductivity. The ionic conductivity of 1D PiHI (with I₂) aligned perpendicular to the electrode, σ_⊥ (15.46 mS cm^-1), is 1.5 times higher than that aligned parallel to the electrode σ_∥ = 10.32 mS cm^-1. The ss-DSSC devices with these self-assembled ordered ionic crystals with a carbazole based sensitizer (SK1) achieved a power conversion efficiency (PCE) of 4.2% and 5.2% for ∥^al and ⊥^ar arrangement, respectively. The reported PCEs are better than that obtained from a classical liquid electrolyte with SK1 sensitizers. The electron kinetics at various interfaces of ss-DSSC devices was evaluated using Electrochemical Impedance Spectroscopy (EIS) measurements. The presence of a saturated cyclic structure promotes close packing through H-bonding and electrostatic interactions, which make ss-DSSC devices more stable up to 600 h under illumination of 1 sun.

Tuning the physical properties of organic sensitizers by replacing triphenylamine with new donors for dye sensitized solar cells - a theoretical approach

New donor molecules with low ionization potential have been theoretically designed by replacing the benzene moieties in triphenylamine (TPA) with thiophene as well as furan. The designed new donors also exhibited planar structure, making an angle of 120° around the nitrogen atom that results in resonance effects through π-bonds of aryl rings. New sensitizers have been theoretically studied using DFT and TD-DFT by adopting these designed donors. UV-Vis absorption spectra, light harvesting ability (LHE) and electron injection ability (ΔG_inject) of the designed sensitizers have been calculated by taking L0 as reference. Orbital overlapping between donor and acceptor facilitates intra-molecular charge transfer, thereby increasing the interfacial electron injection from the sensitizer to the semiconductor nanoparticles. Our theoretical results demonstrate that sensitizers DTPA-AA and DFPA-AA have broader absorption and lower ΔG_inject respectively compare to L0, this opens a new way for designing sensitizers for dye sensitized solar cells (DSSCs). All the dyes designed were found to be good light harvesters.

Stepwise co-sensitization of two metal-based sensitizers: probing their competitive adsorption for improving the photovoltaic performance of dye-sensitized solar cells

How to graft co-sensitizers with different strengths such as LP-2 and N719 onto TiO₂ surfaces for enhancing the performance of dye-sensitized solar cells (DSSCs) has been investigated in detail.

Pyrene based D–π–A architectures: synthesis, density functional theory, photophysics and electron transfer dynamics

Pyrene derivatives show immense potential as sensitizers for dye-sensitized solar cells (DSCs).

Bi-anchoring Organic Dyes that Contain Benzimidazole Branches for Dye-Sensitized Solar Cells: Effects of π Spacer and Peripheral Donor Groups

Benzimidazole-branched bi-anchoring organic dyes that contained triphenylamine/phenothiazine donors, 2-cyanoacrylic acid acceptors, and various π linkers were synthesized and examined as sensitizers for dye-sensitized solar cells. The structure-activity relationships in these dyes were systematically investigated by using absorption spectroscopy, cyclic voltammetry, and density functional theory calculations. The wavelength of the absorption peak was more-heavily influenced by the nature of the π linker than by the nature of the donor. For a given donor, the absorption maximum (λmax ) was red-shifted on changing the π linker from phenyl to 2,2'-bithiophene, whilst the dyes that contained triphenylamine units displayed higher molar extinction coefficients (ϵ) than their analogous phenothiazine-based triphenylamine dyes, which led to good light-harvesting properties in the triphenylamine-based dyes. Electrochemical data for the dyes indicated that the triphenylamine-based dyes possessed relatively low-lying HOMOs, which could be beneficial for suppressing back electron transfer from the conduction band of TiO2 to the oxidized dyes, owing to facile regeneration of the oxidized dye by the electrolyte. The best performance in the DSSCs was observed for a dye that possessed a triphenylamine donor and 2,2'-bithiophene π linkers. Electron impedance spectroscopy (EIS) studies revealed that the use of triphenylamine as the donor and phenyl or 2,2'-bithiophene as the π linkers was beneficial for disrupting the dark current and charge-recombination kinetics, which led to a long electron lifetime of the injected electrons in the conduction band of TiO2 .

Tunable anchoring groups@acridone-linked triphenylamine based pendant chromophores and their effects on the photovoltaic performance as sensitizers for dye-sensitized solar cells

In this study, a series of pendant chromophores bearing methacrylate polymers with different anchoring/acceptor groups were synthesized for use as sensitizers in the dye-sensitized solar cells.

D–D–A dyes with phenothiazine–carbazole/triphenylamine as double donors in photopolymerization under 455 nm and 532 nm laser beams

In order to enhance electron-donating ability, four novel organic dyes (CPC, TPC, CPN and TPN) with double electron donors have been designed and synthesized.

Long-Range π-Conjugation in Phenothiazine-containing Donor-Acceptor Dyes for Application in Dye-Sensitized Solar Cells

Four organic donor-π-bridge-acceptor dyes containing phenothiazine as a spacer and cyanoacrylic acid as an acceptor were synthesized and tested as sensitizers in dye-sensitized solar cells (DSCs). The influence of iodide- and cobalt-based redox electrolytes on the photovoltaic device performance was investigated. In these new dyes, systematic π-conjugation was extended by inserting one or two phenothiazine moieties and investigated within the context of the resulting photoinduced charge-transfer properties. A detailed investigation, including transient absorption spectroscopy and quantum chemical methods, provided important information on the role of extended π-conjugation on the photophysical properties and photovoltaic device performance. Overall, the results showed that the extension of π-conjugation by one phenothiazine unit resulted in the best device performance owing to reduced recombination rates, whereas extension by two phenothiazine units reduced dye adsorption on TiO2 probably owing to the increase in molecular size. The performance of the dyes in DSCs was found to be a complex interaction between dye structure and size.

Influence of the Terminal Electron Donor in D-D-π-A Organic Dye-Sensitized Solar Cells: Dithieno[3,2-b:2',3'-d]pyrrole versus Bis(amine)

With respect to the electron-withdrawing acceptors of D-A-π-A organic dyes, reports on the second electron-donating donors for D-D-π-A organic dyes are very limited. Both of the dyes have attracted significant attention in the field of dye-sensitized solar cells (DSCs). In this work, four new D-D-π-A organic dyes with dithieno[3,2-b:2',3'-d]pyrrole (DTP) or bis(amine) donor have been designed and synthesized for a investigation of the influence of the terminal electron donor in D-D-π-A organic dye-sensitized solar cells. It is found that DTP is a promising building block as the terminal electron donor when introduced in the dithiophenepyrrole direction, but not just a good bridge, which exhibits several characteristics: (i) efficiently increasing the maximum molar absorption coefficient and extending the absorption bands; (ii) showing stronger charge transfer interaction as compared with the pyrrole direction; (iii) beneficial to photocurrent generation of DSCs employing cobalt electrolytes. DSCs based on M45 with the Co-phen electrolyte exhibit good light-to-electric energy conversion efficiencies as high as 9.02%, with a short circuit current density (JSC) of 15.3 mA cm(-2), open circuit voltage (VOC) of 867 mV and fill factor (FF) of 0.68 under AM 1.5 illumination (100 mW cm(-2)). The results demonstrate that N,S-heterocycles such as DTP unit could be promising candidates for application in highly efficient DSCs employing cobalt electrolyte.

2H-[1,2,3]Triazolo[4,5-c]pyridine Cored Organic Dyes Achieving a High Efficiency: a Systematic Study of the Effect of Different Donors and π Spacers

New D-A-π-A-based isomeric sensitizers, PTNn (n = 1-2) and NPTn (n = 1-5), were synthesized using 2H-[1,2,3]triazolo[4,5-c]pyridine (PT) as an auxiliary acceptor, triphenylamine or N,N-bis[4-(hexyloxy)phenyl]aniline as the donor, furan, thiophene, phenyl, or 3-hexylthiophene as the conjugated spacer, and 2-cyanoacrylic acid as the acceptor and anchor as well. They were used as the sensitizers of dye-sensitized solar cells. The NPTn dyes show better performance than the PTNn dyes. Among them, the best efficiency of 7.92% (∼96%, N719) was obtained with the NPT5 dye, indicating that the PT core could be used as a new building block for the design of high-performance sensitizers in the future. The negative Mulliken charge from the auxiliary acceptor was found to be useful as a semiempirical index for correlation of the molecular structure with the cell efficiency among structurally similar D-A-π-A-type congeners.

Benzo[a]carbazole-Based Donor-π-Acceptor Type Organic Dyes for Highly Efficient Dye-Sensitized Solar Cells

A novel class of metal-free organic dyes based on benzo[a]carbazole have been designed, synthesized, and used in dye-sensitized solar cells for the first time. These types of dyes consisted of a cyanoacrylic acid moiety as the electron acceptor/anchoring group and different electron-rich spacers such as thiophene (JY21), furan (JY22), and oligothiophene (JY23) as the π-linkers. The photophysical, electrochemical, and photovoltaic properties, as well as theoretical calculations of these dyes were investigated. The photovoltaic performances of these dyes were found to be highly relevant to the π-conjugated linkers. In particular, dye JY23 exhibited a broad IPCE response with a photocurrent signal up to about 740 nm covering the most region of the UV-visible light. A DSSC based on JY23 showed the best photovoltaic performance with a Jsc of 14.8 mA cm(-2), a Voc of 744 mV, and a FF of 0.68, achieving a power conversion efficiency of 7.54% under standard AM 1.5 G irradiation.

Fluorene-based sensitizers with a phenothiazine donor: effect of mode of donor tethering on the performance of dye-sensitized solar cells

Two types of fluorene-based organic dyes featuring T-shape/rod-shape molecular configuration with phenothiazine donor and cyanoacrylic acid acceptor have been synthesized and characterized as sensitizers for dye-sensitized solar cells. Phenothiazine is functionalized at either nitrogen (N10) or carbon (C3) to obtain T-shape and rod-like organic dyes, respectively. The effect of structural alternation on the optical, electrochemical, and the photovoltaic properties is investigated. The crystal structure determination of the dye containing phenyl linker revealed cofacial slip-stack columnar packing of the molecules. The trends in the optical properties of the dyes are interpreted using time-dependent density functional theory (TDDFT) computations. The rod-shaped dyes exhibited longer wavelength absorption and low oxidation potentials when compared to the corresponding T-shaped dyes attributable to the favorable electronic overlap between the phenothiazine unit and the rest of the molecule in the former dyes. However, the T-shaped dyes showed better photovoltaic properties due to the lowest unoccupied molecular orbital (LUMO) energy level favorable for electron injection into the conduction band of TiO2 and appropriate orientation of the phenothiazine unit rendering effective surface blocking to suppress the recombination of electrons between the electrolyte I3(-) and TiO2. The electrochemical impedance spectroscopy investigations provide further support for the variations in the electron injection and transfer kinetics due to the structural modifications.

N-Annulated perylene-based metal-free organic sensitizers for dye-sensitized solar cells

A series of novel metal-free organic sensitizers based on N-annulated perylene derivatives have been conveniently synthesized, and the DSCs exhibit overall conversion efficiencies ranging from 4.90% to 8.28%.

Molecular design of new organic sensitizers based on thieno[1,4]benzothiazine for dye-sensitized solar cells

A novel thieno[1,4]benzothiazine donor has been developed for the first time to construct metal-free organic sensitizers, which exhibit more dramatically red-shifted absorptions than phenothiazine-based dyes.

The effect of porphyrins suspended with different electronegative moieties on the photovoltaic performance of monolithic porphyrin-sensitized solar cells with carbon counter electrodes

Compared with WH-C3 and WH-C4, the WH-C5-sensitized device shows a significantly enhanced V_oc, J_sc and power conversion efficiency (η).

Cyclometalated ruthenium(ii) complexes with bis(benzimidazolyl)benzene for dye-sensitized solar cells

The length of alkyl chains on the benzimidazole rings of cyclometalated ruthenium dyes is critical to the DSSC performance.

A meso–meso directly linked porphyrin dimer-based double D–π–A sensitizer for efficient dye-sensitized solar cells

A novel double D–π–A branched dye (JY07) was synthesized and applied as a sensitizer for DSSCs.

The effect of different alkyl chains on the photovoltaic performance of D–π–A porphyrin-sensitized solar cells

Compared to the DSSCs based on WH-C1 and YD20 with short alkyl chains, the device sensitized by WH-C2 with the hexyloxy group shows a significantly enhanced V_oc, J_sc and power conversion efficiency (η).