Molecular engineering of organic sensitizers containing indole moiety for dye-sensitized solar cells

Three organic dyes, JK-77, JK-78, and JK-79 containing indole unit are designed and synthesized. Nanocrystalline TiO₂ dye-sensitized solar cells were fabricated using these dyes. Under standard global AM 1.5 solar condition, the JK-79 sensitized solar cell gave a short circuit photocurrent density of 13.62 mA cm⁻², open-circuit voltage of 0.705 V, and a fill factor of 0.74, corresponding to an overall conversion efficiency η of 7.18%. We found that the η of JK-79 was higher than those of other two cells due to the higher V_oc. The improved V_oc value is attributed to the suppression of dark current owing to the blocking effect of a long alkyl chain.     

Controllable hydrothermal synthesis of nanocrystal TiO2 particles and their use in dye-sensitized solar cells

A simple method for the controllable hydrothermal synthesis of nanocrystalline anatase TiO2(nc-TiO2) particles involving the selection of suitable organic alkali peptizing agents is reported.A dye-sensitized solar cell(DSSC) with square-like nc-TiO2 particles with side lengths about 8-13 nm-prepared using tetraethylammonium hydroxide(TEAOH)-in the photoelectrode showed higher photovoltaic performance than two other DSSCs with square-like nc-TiO2 particles with side lengths about 7-10 nm-prepared using tetrabutylammonium hydroxide-or elongated nc-TiO2 particles with lengths about 18-35 nm and width about 10 18 nm-prepared using tetramethylammonium hydroxide(TMAOH)-in the photoelectrodes.When a scattering layer prepared from sub-micron size spheres or cone-like nc-TiO2 particles-synthesized using a higher concentration of TMAOH-was added on top of the photoelectrode fabricated from nc-TiO2 synthesized with TEAOH,the energy conversion efficiency of the DSSC was markedly increased from 6.77% to 8.18%.     

Amphiphilic ruthenium sensitizers and their applications in dye-sensitized solar cells

Amphiphilic ligands 4,4'-bis(1-adamantyl-aminocarbonyl)-2,2'-bipyridine (L(1)), 4,4'-bis[5-[N-[2-(3beta-cholest-5-en-3-ylcarbamate-N-yl)ethyl]aminocarbonyl]]-2,2'-bipyridine (L(2)), 4,4'-bis[5-[N-[2-(3beta-cholest-5-en-3-ylcarbamate-N-yl)propyl]aminocarbonyl]]-2,2'-bipyridine (L(3)), and 4,4'-bis(dodecan-12-ol)-2,2'-bipyridine (L(4)) and their heteroleptic ruthenium(II) complexes of the type [Ru(II)LL(1)(NCS)(2)] (5), [Ru(II)LL(2)(NCS)(2)] (6), [Ru(II)LL(3)(NCS)(2)] (7), and [Ru(II)LL(4)(NCS)(2)] (8) (where L = 4,4'-bis(carboxylic acid)-2,2'-bipyridine) have been synthesized starting from dichloro(p-cymene)ruthenium(II) dimer. All the ligands and the complexes were characterized by analytical, spectroscopic, and electrochemical techniques. The performance of these complexes as charge-transfer photosensitizers in nanocrystalline TiO(2)-based solar cells was studied. When complexes 5-8 anchored onto a 12 + 4 microm thick nanocrystalline TiO(2) films, very efficient sensitization was achieved (85 +/- 5% incident photon-to-current efficiencies in the visible region, using an electrolyte consisting of 0.6 M butylmethylimidazolium iodide, 0.05 M I(2), 0.1 M LiI, and 0.5 M tert-butyl pyridine in 1:1 acetonitrile + valeronitrile). Under standard AM 1.5 sunlight, the complex 8 yielded a short-circuit photocurrent density of 17 +/- 0.5 mA/cm(2), the open-circuit voltage was 720 +/- 50 mV, and the fill factor was 0.72 +/- 0.05, corresponding to an overall conversion efficiency of 8.8 +/- 0.5%.     

Synthesis of organosilicon polymers containing donor-acceptor type π-conjugated units and their applications to dye-sensitized solar cells

Novel organosilicon polymers having donor-acceptor type π-conjugated units in the backbone were prepared by Stille-coupling reactions of bis(tributylstannylthienyl)silanes with diiodoquinoxialine, benzothiadiazole, and benzothiaselenazole. Dehaloganative copolymerization of di(bromothienyl)silanes and dibromoquinoxaline was also studied, which gave the corresponding random copolymer. Applications of these polymers to dye-sensitized solar cells (DSSCs) were examined and it was found that the polymer containing benzoselenadiazole units as the acceptor exhibited the best performance as the sensitizer among the present polymers.     

Rubbery copolymer electrolytes containing polymerized ionic liquid for dye-sensitized solar cells

A novel type of random copolymer comprised of a polymerized ionic liquid, poly(1-((4-ethenylphenyl)methyl)-3-butyl-imidazolium iodide) (PEBII), and amorphous rubbery poly(oxyethylene methacrylate) (POEM) was synthesized and employed as a solid electrolyte in an I₂-free dye-sensitized solar cell (DSSC). The copolymer electrolytes deeply infiltrated into the nanopores of mesoporous TiO2 films, resulting in improved interfacial contact of electrode/electrolyte. The glass transition temperature (T _g) of the PEBII–POEM (?23 °C) was lower than that of PEBII homopolymer (?4 °C), indicating greater chain flexibility in the former. However, the DSSC efficiency of PEBII–POEM (4.5 % at 100 mW/cm²) was lower than that of PEBII (5.9 %), indicating that ion concentration is more important than chain flexibility. Interestingly, upon the introduction of ionic liquid, i.e., 1-methyl-3 propylimidazolium iodide, the efficiency of PEBII remained almost constant (5.8 %), whereas that of PEBII–POEM was significantly improved up to 7.0 % due to increased I^? ion concentration, which is one of the highest values for I₂-free DSSCs.     

Synthesis of carboxylated chlorophyll derivatives and their activities in dye-sensitized solar cells

Chlorophyll-a derivatives possessing a carboxy group in the substituent at the 3-position were prepared by chemical modification of methyl pyropheophorbide-d bearing the 3-formyl group via a Wittig, Barbier-type, or Knoevenagel reaction. The synthetic carboxylated chlorophyll pigments were employed as dye sensitizers for solar cells and their performances were compared in a conventional device based on a mesoporous titanium dioxide electrode and a liquid electrolyte. The solar power conversion efficiency was suppressed with an increase in the length of the oligomethylene moiety between the chlorin π-system and the carboxy group, while a corresponding π-linked ethenylene spacer enhanced the efficiency.     

Anionic benzothiadiazole containing polyfluorene and oligofluorene as organic sensitizers for dye-sensitized solar cells

Anionic polyfluorene and oligofluorene derivatives were synthesized and utilized as organic dye sensitizers in dye sensitized solar cells to show a maximum power conversion efficiency of 1.39%.     

Organic dyes containing a coplanar indacenodithiophene bridge for high-performance dye-sensitized solar cells

A series of new organic dyes exploiting coplanar indacenodithiophene as the central π-spacer of the classical donor-(π-spacer)-acceptor configuration were synthesized and characterized for dye-sensitized solar cells. The coplanarity of the indacenodithiophene core facilitates efficient donor to acceptor charge transfer, imparting the new organic dyes significant bathochromic shifts and remarkable power conversion efficiencies of up to 6.7% (DTInDT) under AM 1.5G radiation.     

Time-varied synthesis of hierarchical ZnO microspheres and their applications in dye-sensitized solar cells

Journal of Solid State Electrochemistry - Hierarchically nano-structured ZnO microspheres have been synthesized solvothermally at variable reaction times (6, 12, 36, and 48 h) by using...     

Zirconium oxide films: deposition techniques and their applications in dye-sensitized solar cells

Zirconium oxide (ZrO₂) is acquiring considerable attention of most of the research groups and leading to a large number of publications due to its unique properties, especially in the context of emerging trends in the third generation of solar cell research. ZrO₂ films offer magnificent aspects related to physicochemical properties, and the properties are found to be dependent on synthesis methods. In the present review, various deposition techniques used to grow zirconium oxide thin films and their application to enhance the quantum efficiency of titanium oxide (TiO₂) based dye-sensitized solar cells (DSSCs) are discussed. Also, the modulated performances of DSSCs fabricated by growing the conformal ZrO₂ insulating films to retard interfacial recombination dynamics on preformed TiO₂ films are discussed.

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Enhanced performance of the dye-sensitized solar cells with phenothiazine-based dyes containing double D-A branches

Double donor-acceptor (D-A) branched dyes (DBD) with a phenothiazine unit as electron donor and a 2-cyanoacrylic acid unit as electron acceptor were synthesized and used as sensitizers for solar cells (DSSCs). The conversion efficiency of the DSSCs amounts up to 4.22% (2.91% for the single D-A branched dye) under AM 1.5 G irradiation. The results show that the performance of DSSCs can be effectively enhanced by the cooperation of two donor-acceptor containing branches in one molecule of the dyes.     

Structural engineering of dipolar organic dyes with an electron-deficient diphenylquinoxaline moiety for efficient dye-sensitized solar cells

A series of new organic dyes containing an electron-deficient diphenylquinoxaline moiety was synthesized and employed as the photosensitizers in dye-sensitized solar cells (DSSCs). The multiple phenyl rings in the peripheral positions of the dye structure provide a hydrophobic barrier to slow down the charge recombination. The photophysical and electrochemical properties of these dyes were investigated in detail. The cell performance and the associated photophysical and electrochemical properties can be easily tuned by the modification of the aromatic fragments within the π spacer. Dye CR204-based DSSC reached the best energy conversion efficiency of 6.49% with an open-circuit voltage of 666 mV, a short-circuit photocurrent density of 14.9 mA cm⁻², and a fill factor of 0.66. The IPCE of CR204-based DSSC covers the light-harvesting to NIR region.     

A dye-sensitized solar cell containing an anchoring porphyrin

We have designed a self-assembly ZnP-ZnPA, based on a porphyrin ZnP bearing 1,3,5-triazine-2,4-diamine unit, and anchoring porphyrin ZnPA. The assembly with ZnP-ZnPA was immobilized on nanostructured TiO₂ electrode surfaces. The assembled structures were characterized by transmission electron microscopy. The optical, photovoltaic, electrochemical impedance spectroscopy, and incident photon-to-current conversion efficiency were measured. The results revealed that the ZnP-ZnPA device had better photovoltaic performance than ZnPA and possessed a higher shortcircuit photocurrent density (J_SC = 6.04) but a lower open-circuit photovoltage (V_OC = 0.51) than anchoring ZnPA. Moreover, our previously reported assembly (ZnP-A1) as reference, the assembly device ZnP-ZnPA had better η (2.24%) and FF (72.7%).     

Theoretical characterization of ruthenium complexes containing functionalized bithiophene ligands for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have gained widespread interest for their potential as low-cost solar energy conversion devices. One of the key issues is the design of higher efficient light-absorbing dyes. In this paper, we present a theoretical characterization of ruthenium complexes containing functionalized bithiophene (btp) ligands (CYC-B1 and CYC-B11) based on density functional theory (DFT) calculations. Molecular geometries, electronic structures, and optical absorption spectra are investigated both in the gas phase and in dimethylformamide (DMF) solution. Frontier orbital analysis shows the three highest HOMOs are composed of nonbonding combinations of the Ru t_2g orbitals with the p orbital and lone pairs of the SCN ligands, while the six lowest LUMOs are the π* combinations of the 4,4’-dicarboxy-2,2’-bipyridine (dcbpy) and/or btp-functionalized bipyridine (bpy) ligands calculated in the gas phase. Inclusion of solvent results in great changes in energies and compositions of the molecular orbitals of these complexes. The spectra are assigned to the intraligand π → π* transitions of the dcbpy ligand in the ultraviolet region, whereas in the visible region the spectra show multitransition character of metal-to-ligand charge transfer (MLCT), interligand π → π*, and intraligand π → π*. Our results clarify the role of the functionalized btp ligands on the absorption properties of the dyes.     

Molecular engineering of organic sensitizers containing p-phenylene vinylene unit for dye-sensitized solar cells

Three organic sensitizers containing bis-dimethylfluorenyl amino donor and a cyanoacrylic acid acceptor bridged by p-phenylene vinylene unit were synthesized. The power conversion efficiency was quite sensitive to the length of bridged phenylene vinylene groups. A nanocrystalline TiO2 dye-sensitized solar cell was fabricated using three sensitizers. The maximum power conversion efficiency of JK-59 reached 7.02%.     

Properties of chemical vapour deposited nanocrystalline TiO2 thin films and their use in dye-sensitized solar cells

Nanocrystalline titanium dioxide (TiO₂) thin films have been prepared using titanium(IV) isopropoxide as a precursor onto the glass and fluorine doped tin oxide coated glass substrates by chemical vapour deposition technique at 400 °C substrate temperature. X-ray diffraction study confirms the polycrystalline nature of TiO₂ with anatase phase having tetragonal crystal structure. The films are 975 nm thick and transparent having transmittance grater than 80%. Atomic force microscopy (AFM) images reveal the nanocrystalline morphology with grain size of 200 nm. The film shows a sharp absorption edge near 350 nm. Photoelectrochemical study shows that TiO₂ thin film sensitized with Brown Orange dye is found to exhibit relatively maximum I_sc and V_oc among the studied dyes. The values of fill factor (FF) and efficiency (η) for the dye-sensitized solar cell (Brown Orange dye-sensitized TiO₂) are 0.54 and 0.17%, respectively. Such films would serve as better prospects for dye-sensitized solar cells.     

Butyronitrile-based electrolyte for dye-sensitized solar cells

We elaborated a new electrolyte composition, based on butyronitrile solvent, that exhibits low volatility for use in dye-sensitized solar cells. The strong point of this new class of electrolyte is that it combines high efficiency and excellent stability properties, while having all the physical characteristics needed to pass the IEC 61646 stability test protocol. In this work, we also reveal a successful approach to control, in a sub-Nernstian way, the energetics of the distribution of the trap states without harming cell stability by means of incorporating NaI in the electrolyte, which shows good compatibility with butyronitrile. These excellent features, in conjunction with the recently developed thiophene-based C106 sensitizer, have enabled us to achieve a champion cell exhibiting 10.0% and even 10.2% power conversion efficiency (PCE) under 100 and 51.2 mW·cm(-2) incident solar radiation intensity, respectively. We reached >95% retention of PCE while displaying as high as 9.1% PCE after 1000 h of 100 mW·cm(-2) light-soaking exposure at 60 °C.     

New architectures for dye-sensitized solar cells

Modern dye-sensitized solar cell (DSSC) technology was built upon nanoparticle wide bandgap semiconductor photoanodes. While versatile and robust, the sintered nanoparticle architecture exhibits exceedingly slow electron transport that ultimately restricts the diversity of feasible redox mediators. The small collection of suitable mediators limits both our understanding of an intriguing heterogeneous system and the performance of these promising devices. Recently, a number of pseudo-1D photoanodes that exhibit accelerated charge transport and greater materials flexibility were fabricated. The potential of these alternative photoanode architectures for advancing, both directly and indirectly, the performance of DSSCs is explored.