Structure-property relationships of organic dyes with D-π-A structure in dye-sensitized solar cells

Organic dyes with a D-π-A structure have drawn increasing attention as sensitizers in dye-sensitized solar cells (DSSCs), due to their rich photophysical properties, easy molecular tailoring, and low-cost production. This review mainly focuses on the relationship between dye structure and photovoltaic properties for organic dyes containing cyanoacrylic acid as both an anchor and an acceptor. This review also introduces different donors and π-conjugation units as building blocks for sensitizer synthesis.     

New D-π-A dyes for efficient dye-sensitized solar cells

Functional organic dyes have promising prospect in dye-sensitized solar cells as a crucial element, of which sensitizers based on donor-π-acceptor are the most important dyes. On the basis of the structures of the aromatic amine donors such as triphenylamine and indoline, this paper reviews the photoelectric conversion properties of organic sensitizers since 2008, and highlights research work in our laboratory in this area.     

The design,synthesis, and characterization of D-π-A-π-A type organic dyes as sensitizers for dye-sensitized solar cells (DSSCs)

New D-π-A-π-A type organic dyes were synthesized and characterized as sensitizers for dye-sensitized solar cells (DSSCs). These dyes showed wide absorption spectra (300–625 nm) and high molar extinction coefficients (ε_467 nm = 60,911 M⁻¹ cm⁻¹). As dye sensitizers in DSSC, the D-π-A-π-A dye having a cyanoacrylic acid as an acceptor gave the best cell performance with a short-circuit photocurrent density (J_sc) of 7.14 mA/cm², an open-circuit voltage (V_oc) of 0.62 V, and a fill factor (FF) of 0.72, corresponding to an overall conversion efficiency η of 3.19%.     

Effects of structure and electronic properties of D-π-A organic dyes on photovoltaic performance of dye-sensitized solar cells

Herein,we examine the performance of dye-sensitized solar cells containing five D-π-A organic dyes designed by systematic modification of π-bridge size and geometric structure.Each dye has a simple push-pull structure with a triarylamino group as an electron donor,bithiophene-4,4-dimethyl-4 H-cyclopenta 1,2-b:5,4-b’]dithiophene(M11),4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophenethiophene(M12),thiophene-4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene(M13),4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene-benzene(M14),and 4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene(M15)units asπ-bridges,and cyanoacrylic acid as an electron acceptor/anchor.The extension of theπ-bridge linkage favors wide-range absorption but,because of the concomitant molecular volume increase,hinders the efficient adsorption of dyes on the TiO₂ film surface.Hence,higher loadings are achieved for smaller dye molecules,resulting in(i)a shift of the TiO₂ conduction band edge to more negative values,(ii)a greater photocurrent,and(iii)suppressed charge recombination between the photoanode and the redox couple in the electrolyte.Consequently,under one-sun equivalent illumination(AM 1.5 G,100 mW/cm²),the highest photovoltage,photocurrent,and conversion efficiency(η=7.19%)are observed for M15,which has the smallest molecular volume among M series dyes.     

Hyperbranched conjugated polymers with donor-π-acceptor architecture as organic sensitizers for dye-sensitized solar cells

Three novel hyperbranched conjugated polymers (H-tpa, H-cya, and H-pca) with the same conjugated core structure and different functional terminal units were synthesized and applied in dye-sensitized solar cells (DSSCs) as photosensitizers. The photophysical, electrochemical and photovoltaic properties of the three hyperbranched conjugated polymers (HBPs) were investigated in detail. The results showed that donor-π-acceptor architecture in hyperbranched molecule benefited intramolecular charge transfer and consequently increased the generation of photocurrent. The three-dimensional (3D) steric configuration of HBPs could effectively suppress the aggregation of dyes on TiO₂ film, which is beneficial for achieving good photovoltaic performances. Among the three hyperbranched dyes, the highest power conversion efficiency (η) of 3.93% (J_sc = 8.78 mA/cm², V_oc = 0.65 V, FF = 0.688) was obtained with a DSSC based on H-pca dye upon the addition of the same mass ratio chenodeoxycholic acid (CDCA) as coadsorbent under AM 1.5 irradiation with 100 mW/cm² simulated sunlight.     

New D-π-A-conjugated organic sensitizers based on α-pyranylidene donors for dye-sensitized solar cells

A series of new push-pull organic dyes incorporating a cyanoacrylic acid group as electron acceptor unit and α-chalcogenopyranylidene group (X = S; O) as electron donor unit has been synthesized, characterized and used as sensitizer for dye-sensitized solar cells (DSSCs). For the first time, α-pyranylidene and thiopyranylidene groups, have been evaluated in DSSC. To obtain the thermodynamic values of the solar cell, an investigation of their electrochemical (CV) and optical properties (UV–vis absorption spectroscopy) is also reported.     

D-π-A dye system containing cyano-benzoic acid as anchoring group for dye-sensitized solar cells

A D-π-A dye (KM-1) incorporating cyano-benzoic acid as a new acceptor/anchoring group has been synthesized for dye-sensitized solar cells (DSCs) with a high molar extinction coefficient of 66,700 M(-1) cm(-1) at 437 nm. Theoretical calculations show that the hydrogen bond between -CN and surface hydroxyl leads to the most stable configuration on the surface of TiO(2). In addition, the adsorption of the dye on TiO(2) follows a Brunauer-Emmett-Teller (BET) isotherm. Multilayer adsorption of KM-1 on TiO(2) seems to take place particularly at higher dye concentrations. DSC device using KM-1 reached a maximum incident photon-to-current conversion efficiency (IPCE) of 84%, with a solar to electric power conversion efficiency (PCE) of 3.3% at AM1.5 G illumination (100 mW cm(-2)). This new type of anchoring group paves a way to design new dyes that combine good visible light harvesting with strong binding to the metal oxide surface.     

Novel D-π-A type II organic sensitizers for dye sensitized solar cells

Four organic donor-π-conjugated-acceptor (D-π-A) type II dyes with different thiophene linkers are reported for dye sensitized solar cells (DSSCs). For the first time, a donor (triphenylamine) was introduced in type II sensitizers, and 2-hydroxybenzonitrile as acceptor/anchoring moiety was covalently linked TiO₂ particles. The dye LS203 in this series gives the best solar energy conversion efficiency of 3.4%, with J_sc = 7.4 mA cm⁻², V_oc = 0.67 V, FF = 0.69, the maximum IPCE value reaches 66.9%.     

Theoretical investigation of nonlinear optical behavior for rod and T-Shaped phenothiazine based D-π-A organic compounds and their derivatives

The exploration of novel materials with excellent nonlinear optical (NLO) features is an area of frontline investigation for scientific community from technological point of view. This study reports the novel phenothiazine-based rod-shaped and T-shaped NLO molecules which are quantum chemically designed from synthesized compounds: rod-shaped (CFA and CBA) and T-shaped (CTA, CCA and CPA). Structural tailoring was performed on D-π-π-A centered CPA chromophore and the effect of various π-spacers, as well as solvents on NLO response properties is investigated. Density functional theory (DFT) along with time dependent DFT (TDDFT) calculations have been executed at B3LYP/6-311G(d,p) functional to examine entire analysis. Results showed a smaller energy gap in structurally modified compounds as compared to reference CPA. Global reactivity parameters analysis revealed smaller hardness and larger softness values in T-shaped compounds. UV–Vis analysis of investigated molecules displayed a red shift in absorption maximum value as compared to CPA. Natural bond orbital (NBO) and frontier molecular orbital (FMO) analysis revealed the stability and intra-molecular electron transferring (ICT) process in investigated molecules. ICT showed the effective charge shift from donor to acceptor via π-spacers. Overall, promising NLO response exists in gas phase and different solvents (acetonitrile, ethyl alcohol and water). Interestingly, proposed molecule CPP presented a maximum value of linear polarizability < α > as 1518.23 a.u and first hyperpolarizability (β_tot) as 755322.39 a.u in acetonitrile solvent. In short, entitled chromophores exhibited excellent NLO properties due to their lower charge transport resistance. This NLO study may open a new topic for researchers to discover novel NLO for hi-tech submissions of modern era.     

New D-π-A-conjugated organic sensitizers based on 4H-pyran-4-ylidene donors for highly efficient dye-sensitized solar cells

We have synthesized a series of four new promising D-π-A conjugated organic sensitizers with a proaromatic 4H-pyran-4-ylidene as a donor, a thiophene ring in the bridge, and 2-cyanoacrilic acid as acceptor. Comparison between different donor substituents and the modification of the thiophene ring resulted in molar extinction coefficients as high as 36399 M(-1) cm(-1) at 551 nm. The photovoltaic properties of the DSSCs demonstrate power conversion efficiencies as high as 5.4%.     

Computational design of new organic (D–π–A) dyes based on benzothiadiazole for photovoltaic applications,especially dye-sensitized solar cells

Research on Chemical Intermediates - A theoretical study on four organic dyes based on bis(4-hexyloxy)triphenylamine as donor and electron acceptor cyanoacrylic acid with a...     

The role of the π linker in donor-π-acceptor organic dyes for high-performance sensitized solar cells

The key elements arising from different linkers between donor (D) and acceptor (A) fragments in D-π-A organic dyes are computationally studied. Taking triarylamine and the cyanoacrylic acid fragments as donor and acceptor units, respectively, the role of the different separators is computationally explored by means of optimized geometries, frontier molecular orbitals, static polarizabilities and hyperpolarizabilities, excitation energies to the lowest excited singlet, the charge-transfer character of the transition, and simulated absorption spectra. The results are compared to two closely related sets of linkers. Electronic-structure calculations on the studied organic dyes are performed with the CIS(D) wave function based method and time-dependent density functional theory (ωB97, ωB97X, and ωPBEh functionals). Solvation effects are introduced with the polarizable continuum model (PCM).     

Novel D-π-A system based on zinc-porphyrin derivatives for highly efficient dye-sensitised solar cells

We have designed and synthesised novel zinc porphyrin dyes that have a D-π-A system based on porphyrin derivatives containing a carbazole linked triphenylamine (TPA) electron-donating group as the second electron donor and a meso-substituted phenyl carboxyl anchoring group attached at the meso position of the porphyrin ring, yielding push-pull porphyrins as the most efficient green dye for DSSC applications. Under photovoltaic performance measurements, a maximum photon-to-electron conversion efficiency of 5.01% was achieved with the DSSC based on the dye HKK-Por1 (J_SC = 10.7 mA/cm², V_OC = 0.67 V, FF = 0.70) under AM1.5 irradiation (100 mW/cm²).     

D-A-π-A organic sensitizers containing a benzothiazole moiety as an additional acceptor for use in solar cells

Three novel triphenylamine-based D-A-π-A-featured dyes (Z1-Z3) have been designed, synthesized and characterized for use in dye-sensitized solar cells. Benzothiazole was incorporated as an additional acceptor, which greatly enhanced the molar extinction coefficient of the dyes. Various conjugated linkers, such as benzene, furan and thiophene, were also introduced to configure the novel D-A-π-A framework in order to prolong electron flow and active transportation. Among all dyes, Z2 containing a thiophene linker exhibited the maximum overall conversion efficiency (η) of 4.16% (Jsc = 9.27 mA cm-2 , Voc = 642 mV, FF = 0.70) under standard global AM 1.5 G solar condition.     

New organic materials based on D–π–A structure for application in dye-sensitized solar cells

Research on Chemical Intermediates - We used density functional theory at B3LYP level with 6-31G(d,p) basis set for all atoms to study the electrochemical, photovoltaic, and absorption properties...     

Novel D-π-A structured Zn(ii)-porphyrin dyes containing a bis(3,3-dimethylfluorenyl)amine moiety for dye-sensitised solar cells

A high solar-to-electricity conversion efficiency of 7.22% was achieved with a short circuit current (J(sc)) of 15.30 mA cm(-2), an open circuit voltage (V(oc)) of 669 mV and a fill factor (FF) of 0.71 for the 2Flu-ZnP-CN-COOH dye with a multi-functional co-adsorbent, under 100 mW cm(-2) AM 1.5 G simulated light.     

Organic dyes based on triphenylamine for dye-sensitized solar cells:Structure–property relationships

Three new organic dyes based on triphenylamine with a structure of A-D-A-D-A(D1),A-D-A(D2) and D-A(D3) were designed,theoretically calculated and synthesized for dye-sensitized solar cells.Dye D1 exhibits a broader absorption than D2 and D3,due to the intramolecular charge transfer between the donor triphenylamine and the acceptor benzothiadiazole.Dye D1 exhibits a lower HOMO and a lower LUMO than D2 and D3 due to the electron-withdrawing benzothiadiazole.The number of anchoring group cyanoacrylic acid has no obvious influence on absorption and energy levels of D2 and D3.The LUMO of D1 locates on benzothiadiazole rather than cyanoacrylic acid anchoring groups,while the LUMOs of D2 and D3 are localized on cyanoacrylic acid.D2 and D3 give higher short-circuit current density than D1.D3 with one anchoring group gives the highest open-circuit voltage.Consequently,the D3-based device gives the highest efficiency.     

Design and synthesis of D-π-A fluorescent dyes based on nicotinonitrile and azobenzene derivatives

Study the synthesis and fluorescent properties of a new series of D-π-A fluorescent dyes based on nicotinonitrile and azobenzene is the main objective for this work. Reduction with Zn/HCl, diazotization with HCl/NaNO₂, and coupling using catalytic NaOH or AcONa are simple applied methods. Where, nicotinonitrile 3 was synthesized via reduction of nitro derivative 1 followed by diazotization with HCl/NaNO₂ in acetic acid. The formed benzene diazonium chloride was coupled with several activated phenols, aniline, and α-CH acids to yield the respective azo dyes 4-11 in moderate to good yield. Dyes 11a-d subjected to intermolecular cyclization with hydrazine hydrate resulted in pyrazole dyes 12-15 in moderate yield. Dyes containing pyrazole moiety or electron-withdrawing groups at the sixth position of pyridine nucleus exhibit stronger blue-green emission (λ_fl.max = 503, 507, 500, 501, 502, 493, and 514 nm) than that of the rest of compounds.     

A novel D-A-π-A organic sensitizer containing a diketopyrrolopyrrole unit with a branched alkyl chain for highly efficient and stable dye-sensitized solar cells

A novel D-A-π-A type organic dye (YCD01) incorporating a diketopyrrolopyrrole unit with a branched alkyl chain was synthesized for dye-sensitized solar cells. YCD01 showed a high conversion efficiency of 7.43% (AM 1.5, 100 mW cm(-2)) with a J(sc) of 13.40 mA cm(-2), a V(oc) of 0.76 V, a FF of 0.73 and an excellent stability.     

2Rotaxane based on terpyridyl bimetal ruthenium complexes and β-cyclodextrin as organic sensitizer for dye-sensitized solar cells

The conjugated carboxy-functionalized terpyridyl bimetal ruthenium complex [(tdctpy)Ru(dctpy-(ph)₄-dctpy)Ru(tdctpy)][PF₆]₄ and [2]rotaxane by self-assembly of [(tdctpy)Ru(dctpy-(ph)₄-dctpy)Ru(tdctpy)][PF₆]₄ with β-cyclodextrin are reported as sensitizer for dye-sensitized solar cells (DSSCs), where tdctpy?=?4′-p-tolyl-4,4″-dicarboxy-2,2′?:?6,2″-terpyridine, dctpy?=?4,4″-dicarboxy-2,2′?:?6,2″-terpyridine and dctpy-(ph)₄-dctpy represents a bridging ligand where two 4,4″-dicarboxy-2,2′?:?6′,2″-terpyridine units are connected through four phenyl spacers in the 4′-position. The DSSCs fabricated utilizing these materials give typical electric power conversion efficiency of 0.013–0.523% under air mass (AM) 1.5, 100?mW?cm^?2 irradiation at room temperature. The terpyridyl bimetal ruthenium complex [(tdctpy)Ru(dctpy-(ph)₄-dctpy)Ru(tdctpy)][PF₆]₄ with conjugated-bridge chains displayed much higher conversion efficiency compared with the carboxy-functionalized terpyridyl monometal ruthenium complex [tdctpy-Ru-(idctpy)][PF₆]₂, where idctpy?=?4′-p-iodophenyl-4,4″-dicarboxy-2,2′?:?6,2″-terpyridine. [2]Rotaxane displayed the highest electric power conversion efficiency of 0.523% when β-cyclodextrin was introduced into the conjugated terpyridyl bimetal ruthenium complex and formed [2]rotaxane.