Dye-sensitized solar cells based on donor-π-acceptor fluorescent dyes with a pyridine ring as an electron-withdrawing-injecting anchoring group

A new‐type of donor–acceptor π‐conjugated (D‐π‐A) fluorescent dyes NI3 – NI8 with a pyridine ring as electron‐withdrawing‐injecting anchoring group have been developed and their photovoltaic performances in dye‐sensitized solar cells (DSSCs) are investigated. The short‐circuit photocurrent densities and solar energy‐to‐electricity conversion yields of DSSCs based on NI3 – NI8 are greater than those for the conventional D‐π‐A dye sensitizers NI1 and NI2 with a carboxyl group as the electron‐withdrawing anchoring group. The IR spectra of NI3 – NI8 adsorbed on TiO₂ indicate the formation of coordinate bonds between the pyridine ring of dyes NI3 – NI8 and the Lewis acid sites (exposed Tiⁿ⁺ cations) of the TiO₂ surface. This work demonstrates that the pyridine rings of D‐π‐A dye sensitizers that form a coordinate bond with the Lewis acid site of a TiO₂ surface are promising candidates as not only electron‐withdrawing anchoring group but also electron‐injecting group, rather than the carboxyl groups of the conventional D‐π‐A dye sensitizers that form an ester linkage with the Brønsted acid sites of the TiO₂ surface.     

Novel π-conjugated structures with fluorescent properties based on 4-alkoxytetrahydroquinazoline N-oxide

Russian Chemical Bulletin - Synthetic approaches to previously unknown 4-OR-2-methyltetrahydroquinazoline N-oxides were elaborated. 4-Alkoxy- and 4-aryloxy-2-methyltetrahydroquinazoline N-oxides...     

Bright, color-tunable fluorescent dyes based on π-expanded diketopyrrolopyrroles

A synthetic approach to the structurally diverse family of π-expanded diketopyrrolopyrroles is described. A three-step strategy appears to be very general and starts with the preparation of diketopyrrolopyrroles followed by N-alkylation with bromoacetaldehyde diethyl acetal and electrophilic aromatic substitution. The final reaction regioselectively furnishes S-shaped, violet and blue functional dyes of previously unknown structure. New dyes possess sharp absorption and emission peaks, with very high molar absorption coefficients and reasonable fluorescence quantum yields. As a proof of principle, cell uptake of selected dye was demonstrated.     

Panchromatic ruthenium sensitizer based on electron-rich heteroarylvinylene π-conjugated quaterpyridine for dye-sensitized solar cells

The first example of a heteroarylvinylene π-conjugated quaterpyridine Ru(II) sensitizer (N1044) was synthesized and used in dye-sensitized solar cells; the dye has an effective panchromatic absorption band, covering the entire visible spectrum up to the NIR region, and superior electrochemical characteristics (HOMO/LUMO and bandgap energies) with respect to previous representative Ru(II) bi- and quaterpyridine sensitizers. A record IPCE curve ranging from 360 to 920 nm has been measured with a maximum of 65% at 646 nm and still 33% efficiency at 800 nm; this leads to substantially increased photocurrent (19.2 mA cm(-2)) when compared to the prototype N719 Ru(II) sensitizer.     

Efficient solar cells based on cosensitizing porphyrin dyes containing a wrapped donor,a wrapped π-framework and a substituted benzothiadiazole unit

Three new porphyrin dyes XW45-XW47 have been synthesized employing a dialkoxy-wrapped phenothiazine donor, a tetraalkoxy-wrapped porphyrin π-framework, a benzothiadiazole(BTD)-based auxiliary acceptor, and an anchoring benzoic acid group. On the basis of our previously reported dye XW36, XW45 was synthesized by introducing a BTD unit to broaden the absorption spectrum, further introducing a hexyl-substituent into the BTD unit afforded XW46, and an additional fluorine atom was introduced to the carboxyphenyl acceptor to afford XW47. As expected, the BTD unit obviously broadens and red-shifts the absorption threshold of XW45-XW47 to ca.750 nm. Dye-sensitized solar cells(DSSCs) were fabricated based on a cobalt electrolyte using chenodeoxycholic acid(CDCA) as the coadsorbent. Under full sun illumination, XW45 exhibits an efficiency of 9.73%, which is slightly lower than that of 10.19% obtained for the reference dye SM315. By contrast, XW46 and XW47 show higher efficiencies than SM315 owing to the improved anti-aggregation ability associated with the hexyl group on the BTD unit and better ICT effect induced by the fluorine atom on the carboxyphenyl unit. Thus, XW47 exhibits the highest efficiency of 10.41% among the porphyrin dyes. Furthermore, PT-C6 was used as the cosensitizer to improve the light harvesting ability and efficiencies of the cells due to its broad absorption within 350–560 nm. Thus, high efficiencies of 10.32%, 11.38% and 10.90% were achieved for the cosensitized solar cells based on XW45–XW47, respectively, owing to the obviously enhanced photocurrent density(JSC). In addition, under 30% full sun illumination, XW46+PT-C6 exhibits a high efficiency of 13.08%. These results give an effective method for building high performance DSSCs through the cosensitization of porphyrin dyes containing a wrapped donor, a wrapped porphyrin framework and a properly substituted auxiliary benzothiadiazole unit.     

Molecular engineering and cosensitization for developing efficient solar cells based on porphyrin dyes with an extended π framework

<正>Dye-sensitized solar cells(DSSCs)have a promising future because of their low production cost,easy fabrication and relatively high solar energy conversion efficiency.In the past two decades,increasing interests have been focused on the improvement of cell efficiencies.Thus,many efficient sensitizers with donor-π-acceptor frameworks have been successfully developed.In this respect,porphyrins have     

Near-infrared absorbing squarylium dyes with linearly extended π-conjugated structure for dye-sensitized solar cell applications

A novel class of near-infrared absorbing squarylium sensitizers with linearly extended π-conjugated structures, which were obtained by Pd-catalyzed cross-coupling reactions with stannylcyclobutenediones, has been developed for dye-sensitized solar cells. The cells based on these dyes exhibited a significant spectral response in the near-infrared region over 750 nm in addition to the visible region.     

Triphenylamine/tetracyanobutadiene-based D-A-D π-conjugated systems as molecular donors for organic solar cells

Thiophene-based D-A-D π-conjugated systems containing triphenylamine end groups connected to a 1,1,4,4-tetracyanobuta-1,3-diene acceptor by oligothiophene chains of variable length have been synthesized. These compounds show interesting light-harvesting properties and low-lying HOMO levels. Preliminary results on bilayer heterojunction solar cells with C(60) as acceptor show power conversion efficiency higher than 1.0%.     

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.     

Charge dynamics in solar cells with a blend of π-conjugated polymer-fullerene studied by transient photo-generated voltage

The biphasic feature of transient photo-generated voltage (TPV) is investigated in organic solar cells (OSCs) with a blend active layer of poly(3-hexylthiophene) (P3HT) and phenyl C61 butyric acid methyl ester (PCBM). The positive and negative components in biphasic TPV are explained through PCBM only and P3HT only devices. The negative and positive components are ascribed to the dipole formation at the buried interface of P3HT/indium tin oxide (ITO) and PCBM/ITO respectively. Based on these findings, two fundamental phenomena are revealed as follows: (1) interfacial modification on the buried interface inverts the negative component in biphasic TPV to a positive component, which prevents the leakage current channel in the conventional OSC structure; and (2) the solvent chosen transforms the positive component in biphasic TPV into a negative signal, which blocks the leakage current channel in the inverted OSC structure. Consequently, the study of TPV polarity provides the justification of the interaction at the buried interface. Besides, the decay of TPV is found to be bi-exponential, which can be used as a tool to estimate the degree of charge balance in OSCs.     

Tandem phospha-Friedel-Crafts reaction toward curved π-conjugated frameworks with a phosphorus ring junction

The tandem phospha-Friedel-Crafts reaction transforms dichloro(m-teraryl)phosphine to the corresponding triarylphosphine derivatives containing curved π-conjugated frameworks with a phosphorus ring junction. The rigid molecular frameworks enable these unprecedented phosphine compounds to hold an extended π-conjugation spread over the whole molecule.     

Reactivity of functional detergents with a pyridine ring and an α-nucleophile fragment in the head group

Functional detergents (FD) based on pyridine and containing aldoximate, ketoximate, and hydroxamate groups were synthesized. Their reactivity in FD/CTAB comicelles toward 4-nitrophenyl 4-toluenesulfonate (NPTS), diethyl phosphate (NPDEP), and diethylphosphonate (NPDEPS) in weakly alkaline media was investigated. Functional detergents based on pyridine are effective in the decomposition of ecotoxicants; the half-lives for the transformation of the substrates into the reaction products in the presence of a functional detergent containing, for example, a ketoximate group amounts to ∼40 s (NPTS), ∼120 s (NPDEP), and ∼5 s (NPDEPS). By analyzing the results it was possible to establish the paths to further modification of the head group of the surfactant, i.e., by varying the structure of the oximate group at various positions of the pyridinium ring aimed at the production of low-basicity functional detergents. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 284–291, September–October, 2008.     

Synthesis of π-conjugated, pyridine ring functionalized bis-terpyridines with efficient green, blue, and purple emission

A large variety of rigid, π-conjugated, pyridine ring functionalized bis-terpyridines are synthesized efficiently using tandem Miyaura/Suzuki-type cross-coupling reaction. Photophysical property study reveals that the absorption and luminescent properties of the obtained bis-terpyridines are profoundly affected by the nature of the functional groups at the peripheral pyridine and the spacers. Namely, by tailoring precisely the structures, the light-emitting efficiencies of bis-terpyridines can be enhanced significantly with quantum yields (Φ_f) of up to 0.62, and the emission colors can be tuned to display distinct colors including purple, bright blue, and bright green. Consequently, the novel bis-terpyridines are attractive ligands for the assembly of new metallo-supramolecule based functional materials.     

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.     

Wide bandgap conjugated polymers based on bithiophene and benzotriazole for bulk heterojunction solar cells: Thiophene versus thieno[3,2-b]thiophene as π-conjugated spacers

Two wide bandgap (WBG) conjugated polymers, P2T-DTTTAZ and P2T-DTTAZ, with donor-π-acceptor (D-π-A) structures was designed and synthesized, utilizing thieno[3,2-b]thiophene (TT) and/or thiophene (T) units as π-bridge in conjugated polymer backbone. And, the wider optical band gap (E_g) of approximately 1.98 eV for P2T-DTTTAZ and 2.09 eV for P2T-DTTAZ were observed. Obviously, replacing T unit with larger conjugated plane TT unit as π-bridges, P2T-DTTTAZ resulted in the red shifted absorption and the reduced band gap, compared with these of P2T-DTTAZ. The polymer solar cells (PSCs) with an inverted device structure based on P2T-DTTTAZ or P2T-DTTAZ as donor and [6,6] phenyl-C₆₁ butyric acid methyl ester (PC₆₁BM) as acceptor were assembled and the photovoltaic properties were also investigated. The power conversion efficiencies (PCEs) of 1.57% for P2T-DTTTAZ and 1.25% for P2T-DTTAZ were obtained.     

Pyrene-based organic dyes with thiophene containing π-linkers for dye-sensitized solar cells: optical, electrochemical and theoretical investigations

A new series of metal-free organic dyes containing pyrene and α-cyanoacrylic acid end groups and thiophene, bithiophene, thienylbenzene or thienylfluorene π-linkers were synthesized and characterized by absorption, emission and electrochemical measurements. Time-dependent density functional theoretical calculations were also performed to unravel the nature of the absorption induced electronic excitations. Extension of conjugation in the π-linker by the incorporation of phenyl or fluorene was found to enhance the molar extinction coefficient while the use of thiophene red-shifted the absorption. The longer wavelength absorption peaks found for the dyes were attributed to π-π* transition with a contribution from the charge transfer transition which becomes prominent for the bithiophene bridged derivative. The bithiophene containing dye showed moderate overall light-to-electron conversion efficiency attributable to the favorable absorption and redox properties originating due to the presence of a bithiophene segment. The trends observed for the various dyes in the device performance were rationalized by electron-impedance spectroscopy measurements.     

Synthesis and photophysical properties of five-membered ring π-conjugated materials based on bisthiazol-2-yl-amine and their metal complexation studies

Poly(5,5′-(2-hexyldecyl)-bisthiazol-2-yl-amine) (PBTA) is prepared by nickel(0) mediated Yamamoto-type coupling. The photoluminescence (PL) spectrum of PBTA in THF solution displays pure blue emission with a peak centered at 444 nm without any shoulder peaks and the HOMO and LUMO values for PBTA are estimated to be 5.11  and 2.90 eV, respectively. In addition, we have synthesized a novel bisthiazol-2-yl-amine (BTA)-cored donor-acceptor (D-A) chromophore system, namely 5-(4-(diphenylamino)phenyl)-N-(5-(4-(diphenylamino)phenyl)thiazol-2-yl)-N-octylthiazol-2-amine (2-TPA-BTA) in which the electron-donating (D) moiety is triphenylamine group and the electron-withdrawing (A) unit is thiazole group. Furthermore, in this report, we present the complexation studies of both the BTA and 2-TPA-BTA chromophores with Cu(II) and Pd(II), respectively. The crystal structures are established by single-crystal X-ray diffraction analysis. These studies not only provide the general photophysical principles of the materials based on BTA moiety but also encourage progress toward realizing the full potential of its hybrid metal-organic frameworks.     

Investigating the effect of π-configurations and methoxy substitution on donor and π- spacers based dyes for dye-sensitized solar cell applications–computational approach

Research on Chemical Intermediates - Triphenylamine and methoxy substituted triphenylamine-based dyes are examined by density-functional theory and time-dependent density-functional theory. The...     

Theoretical investigation of novel carbazole-fluorene based D-π-A conjugated organic dyes as dye-sensitizer in dye-sensitized solar cells (DSCs)

The ground state structure and frontier molecular orbital of newly synthesized carbazole-fluorene based D-π-A organic dyes, CFP1A, CFP2A, CFP1CA, and CFP2CA, were theoretically investigated using density functional theory (DFT) at B3LYP/6-31G(d,p) level. These dye molecules have been constructed based on carbazole-fluorene as the electron-donating moiety while introducing benzene units as π-spacer connected to different anchor groups, such as acrylic acid and cyanoacrylic acid, as acceptors. The electronic vertical excitation energies and absorption wavelength were carried out using time-dependent DFT (TD-DFT). Furthermore, the adsorptions of phenylacrylic acid and phenylcyanoacrylic acid on the TiO(2) anatase (101) surface were carried out by means of quantum-chemical periodic calculations employing periodic PBE functional with DNP basis set. The results promise that anchor dyes with strong withdrawing CN group have easier injected electron to the conduction band of semiconductor implying that CFP1CA and CFP2CA show better performance among four dyes. Additionally, the intramolecular charge transfers (ICT) from electron donor group to anchoring group of CFP1CA and CFP2CA have shown better performance. The calculated results provide the efficiency trend of our new dyes as CFP1CA ≈ CFP2CA > CFP1A ≈ CFP2A which are excellently agree with experimental observation.