Mechanisms of suppression and enhancement of photocurrent/conversion efficiency in dye-sensitized solar-cells using carotenoid and chlorophyll derivatives as sensitizers

The mechanisms of suppression and enhancement of photocurrent/conversion efficiency (performance) in dye-sensitized solar cells, using carotenoid and chlorophyll derivatives as sensitizers, were compared systematically. The key factor to enhance the performance was found to be how to minimize interaction among the excited-state dye-sensitizer(s). In a set of retinoic-acid (RA) and carotenoic-acid (CA) sensitizers, having n conjugated double bonds, CA7 gave rise to the highest performance, which was reduced toward RA5 and CA13. The former was ascribed to the generation of triplet and the resultant singlet-triplet annihilation reaction, while the latter, to the intrinsic electron injection efficiency. In a set of shorter polyene sensitizers having different polarizabilities, the one with the highest polarizability (the highest trend of aggregate formation) exhibited the higher performance toward the lower dye concentration and the lower light intensity, contrary to our expectation. This is ascribed to a decrease in the singlet-triplet annihilation reaction. The performance of cosensitization, by a pair of pheophorbide sensitizers without and with the central metal, Mg or Zn, was enhanced by the light absorption (complementary rather than competitive), the transition-dipole moments (orthogonal rather than parallel) and by the pathways of electron injection (energetically independent rather than interactive).     

Photoinduced anchoring transitions in a nematic doped with azo dyes

Recently, we reported on a light-induced anchoring transition of an azobenzene nematic from planar to homeotropic alignment. In the proposed model of the transition, the changes in shape of the liquid crystal molecules and of their net dipole moment, due to the photoisomerization, were considered to play a vital role in the occurrence of the transition. In order to assess the validity of this model, a study of the anchoring behaviour of nematic guest-host liquid crystal mixtures containing two photochromic dyes, 3,3'- and 4,4'-substituted azobenzenes, was carried out. The dyes have very similar molecular structures to that of the azobenzene nematic previously studied, and their molecules, having a linear shape in the trans-form, maintained this shape after photoisomerization in the case of the 3,3'-azo dye, and changed it to bent in the case of the 4,4'-azo dye. The dyes possessed similar net dipole moments that increased substantially after photoisomerization, resulting in a preferential adsorption of their cis-isomers on the solid substrate. However, only the mixture containing the 4,4'-azo dye exhibited an anchoring transition from planar to homeotropic alignment upon illumination with unpolarized UV light, a behaviour in excellent agreement with the prediction of the model for the light-induced anchoring transition. An anchoring transition from random planar to uniform planar alignment was found to take place in the mixtures when linearly polarized UV light was used, requiring, however, a different exposure time for the two dyes.     

Photoinduced anchoring transitions in a nematic doped with azo dyes

Recently, we reported on a light-induced anchoring transition of an azobenzene nematic from planar to homeotropic alignment. In the proposed model of the transition, the changes in shape of the liquid crystal molecules and of their net dipole moment, due to the photoisomerization, were considered to play a vital role in the occurrence of the transition. In order to assess the validity of this model, a study of the anchoring behaviour of nematic guest-host liquid crystal mixtures containing two photochromic dyes, 3,3'- and 4,4'-substituted azobenzenes, was carried out. The dyes have very similar molecular structures to that of the azobenzene nematic previously studied, and their molecules, having a linear shape in the trans-form, maintained this shape after photoisomerization in the case of the 3,3'-azo dye, and changed it to bent in the case of the 4,4'-azo dye. The dyes possessed similar net dipole moments that increased substantially after photoisomerization, resulting in a preferential adsorption of their cis-isomers on the solid substrate. However, only the mixture containing the 4,4'-azo dye exhibited an anchoring transition from planar to homeotropic alignment upon illumination with unpolarized UV light, a behaviour in excellent agreement with the prediction of the model for the light-induced anchoring transition. An anchoring transition from random planar to uniform planar alignment was found to take place in the mixtures when linearly polarized UV light was used, requiring, however, a different exposure time for the two dyes.     

染料敏化太阳能电池中二聚噻吩类光敏染料构效关系的理论研究

D-π-A型有机光敏染料结构上的微小差异会引起器件性能的显著不同. 为了合理解释染料分子1和2(给体分别为咔唑和二氢吲哚)结构与性能之间的关系, 采用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)讨论了包括紫外-可见吸收光谱、 光捕获效率、 电子注入驱动力、 垂直方向偶极矩和电子转移数目在内的一系列影响染料性能的理论参数. 结果表明, 在光捕获效率和电子注入效率差别不大的情况下, 染料分子2较低的染料再生效率可导致其短路电流较小; 同时, 在由光诱导产生的从染料分子转移到半导体的电子数目以及电子复合程度相差不大的情况下, 染料分子1垂直方向上较大的偶极矩则可导致其具有较高的开路电压. 计算结果与实验值相吻合, 有望对今后设计合成高效光敏染料提供一定的理论指导.     

Photoinduced electron transfer at liquid|liquid interfaces. Part VII. Correlation between self-organisation and structure of water-soluble photoactive species

The self-organisation of a variety of dyes at the water|1,2-dichloroethane interface was studied by admittance measurements, photocurrent–potential curves and light polarisation anisotropy of the photocurrent. The heterogeneous photo-oxidation of ferrocene was studied at interfaces sensitised by Sn(IV) meso-tetra-(4-carboxyphenyl) porphyrin dichloride (SnTPPC), chlorin e-6, protoporphyrin IX (protoIX) and Fe(III) protoporphyrin IX chloride (Fe-protoIX). Cyclic voltammograms and capacitance voltage curves exhibit different features associated with the self-assembly of the dye species at the liquid|liquid boundary. In the case of SnTPPC, the capacitance curves displayed the characteristic responses commonly associated with the specific adsorption of ionic species. On the other hand, chlorin e-6, protoIX and Fe-protoIX show rather complex behaviour suggesting not only changes in the excess charge but also in the dielectric permittivity of the interface. Differences in the photocurrent efficiency were also observed under the same experimental conditions. The relative magnitude of the photocurrent responses were rationalised in terms of the phenomenological electron transfer rate constant, the photon capture cross-sections and the lifetime of the triplet state as obtained from nanosecond flash photolysis. Finally, the average molecular orientation of the adsorbed photoactive species was estimated from the photocurrent dependence on the angle of light polarisation in total internal reflection. The results show a clear correlation between the orientation of the transition dipole and the distribution of the peripheral carboxyl groups responsible for the hydrophilic nature of the dyes.     

Optical Sensing by Silica/Titania Thin Films Doped with Oxacarbocyanine Dye

Photocurrent responses of sol-gel films of silica/titania doped with oxacarbocyanine dye were investigated with a sandwich-type photocell constructed with polymer electrolyte membrane and indium-tin-oxide glass electrodes. At an equilibrium and positive bias voltages, a typical photocell exhibited negative and positive current peaks when the visible light illumination was on and off, respectively. The wavelength dependence of the photocurrent responses well matched to the absorption band of the doped dye. This differential photocurrent response was attributed to trapping of carriers photoexcited in the dye molecules at the defect states in the matrix film. At negative bias voltages, on the other hand, the cell exhibited constant, negative photoelectrochemical currents under illumination. These differential and linear photocurrent responses were affected by the SiO₂/TiO₂ matrix structures depending on the Si : Ti ratio.     

Electron microscopy studies on the coil-to-globule transition of a polyelectrolyte in a water–acetone mixture

A high molar mass polycation poly(methacryloylethyl trimethylammonium methylsulphate), PMETMMS, dissolved in mixtures of water and acetone, was studied using light scattering during the reversible coil-to-globule transition. When the mass fraction of acetone in the solvent mixture, γ, is higher than 0.80, PMETMMS adopts a globular state but does not aggregate. The collapse of PMETMMS can also be induced by the dilution of the polymer solution, if 0.70 ≤ γ < 0.80, and the solvent composition is kept constant. The results obtained by light scattering have been confirmed using a transmission electron microscope with which the collapse of PMETMMS has been observed. At high polymer concentration and 0.70 ≤ γ < 0.80, a transient network is formed: coils strongly interact with each other via dipole–dipole interactions in a thermodynamically poor solvent. At low concentration regime when 0.70 ≤ γ < 0.80, or in solutions with the mass fraction of acetone higher than 0.80, all the PMETMMS molecules are collapsed. In the intermediate region, the collapse of PMETMMS is gradual and coils, globules, as well as fragments of the network coexist in the solution. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3337–3343, 1999     

Multifunctional Molecular Material Combining Photocurrent Generation and Second-Order Optical Nonlinearity in LB Monolayer Films

ＩｎｔｒｏｄｕｃｔｉｏｎＭｏｌｅｃｕｌａｒｎｏｎｌｉｎｅａｒｏｐｔｉｃｓ (ＮＬＯ)ｈａｓａｔｔｒａｃｔｅｄｉｎ ｃｒｅａｓｉｎｇｉｎｔｅｒｅｓｔｏｖｅｒｔｈｅｐａｓｔｔｅｎｙｅａｒｓ ,ｂｅｃａｕｓｅｏｆｔｈｅｉｒｐｏｔｅｎｔｉａｌａｐｐｌｉｃａｔｉｏｎｓｉｎｖａｒｉｏｕｓｆｉｅｌｄｓｉｎｃｌｕｄｉｎｇｔｅｌｅｃｏｍ ｍｕｎｉｃａｔｉｏｎｓ ,ｏｐｔｉｃａｌｄａｔａｓｔｏｒａｇｅａｎｄｐｒｏｃｅｓｓｉｎｇａｎｄｏｐｔｉ ｃａｌｐｏｗｅｒｌｉｍｉｔａｔｉｏｎ .1,2 Ｉｔｉｓｗｅｌｌｋｎｏｗｎｔｈａｔｔｈｅｐ…     

Anomalous photoconductivity effects of poly-N-epoxypropylcarbazole films with a high concentration of an anionic polymethine dye

Photoluminescence quenching in an external electric field increases and a long-wavelength photoluminescence band and photoconductivity appear in the visible spectrum with increasing concentration of anionic polymethine dye in poly-N-epoxypropylcarbazole films. Associated species containing dye ion pairs are formed with increasing dye concentration. The kinetics found for the growth and relaxation of the photocurrent in these composite films is anomalous for photosemiconductor materials: the time required for growth of the photocurrent is much greater than the time for its relaxation after switching off the light. A prior irradiation memory effect of the films was discovered.     

Effects of tethering alkyl chains for amphiphilic ruthenium complex dyes on their adsorption to titanium oxide and photovoltaic properties

Ruthenium (II) complex dye, Ru(4,4'-dicarboxyl-2,2'-bipyridine)(4-nonyl-2,2'-bipyridine) (NCS)(2), (denoted as RuC9) tethering single alkyl chain was synthesized and well characterized. Its adsorption behavior onto the mesoporous TiO(2) and photovoltaic properties were compared with Z907 which has similar chemical structure but tethers two alkyl chains. RuC9 dyes tend to aggregate into vesicles in the acetonitrile/t-butanol co-solvent as a result of the amphiphilic structure, whereas Z907 dyes aggregate into lamellae. The dye-sensitized solar cell (DSSC) with RuC9 dye showed higher short-circuit photocurrent than that with Z907, attributing to its higher molar optical extinction coefficient and more adsorption amount onto the mesoporous TiO(2). However, the DSSC with Z907 dye has higher open-circuit photovoltage and power conversion efficiency, presumably due to the fact that Z907 with more alkyl chains formed a molecular layer with higher hydrophobicity. It reduced the charge recombination in the interface between the dye-sensitized mesoporous TiO(2) and electrolyte as verified by the electrochemical impedance spectroscopy and intensity modulated photocurrent and photovoltage spectroscopies.     

Light absorption at high intensities. Comparison of quantum theory and semi-classical results

An error in the author's previous treatment of the interaction of an absorber with high intensity light is noted. The correct development of Mower is applied to determine the amplitude of the initial state of the radiation-matter system. Comparison of the quantum theory solution for a damped absorber exposed to a square light pulse with the results of semiclassical theories based on the undamped optical Bloch equations is effected by determining the effective in- and out-of-phase components of the transition dipole response. In general, the out-of-phase (or absorptive) part of the transition dipole is zero at the outset and strongly time-dependent at short times, evolving to a steady-state value at longer times. For resonance radiation the system exhibits either overdamped irreversible decay or underdamped oscillations, depending upon the relative magnitudes of the incident light intensity and the radiative damping rate. Specific results are presented for a variety of limiting values of the physical parameters, including light intensity, damping rate, and amount of off-resonance.     

Electrochromism of merocyanine dyes as detector of internal charges in sandwich arrangements with molecular crystals

The photosensitized charge transfer reaction from a merocyanine dye laser to a p-chloranil single crystal is studied. It was found that the maximum of the action spectrum of the photocurrent shifts by several nanometers when the externally applied voltage or the illuminating light level is increased. A model is proposed which interprets these observations as being due to the induced electric field of a layer of ionized dye molecules at the very surface of the single crystal.     

Bacterial photosynthesis begins with quantum-mechanical coherence

In the antenna system of photosynthetic bacteria, pigments form circular aggregates whose excitations are excitons with quantum-mechanical coherence extending over many pigments. These excitons play crucial roles in light harvesting, storage, and excitation-energy transfer (EET). EET takes place rapidly to and/or from optically forbidden exciton states, without total transition dipole, within the antenna system and to the reaction center. Such EETs cannot be rationalized by F?rster's formula, the traditional theory on EET, because it allows EET only between optically allowed states. The coherence in the excitons seems to prohibit rapid EET on this formula. The bacteria overcome this difficulty by circumventing the coherence, using the effects of the physical size of an aggregate that is larger than the shortest distance between pigments in the donor and pigments in the acceptor. The shortest-distance pair therein cannot detect whether the aggregate has a nonvanishing total transition dipole or not, since the pair see effectively only the transition dipole on the other pigment in themselves. The transition dipole facilitates rapid EET even to and/or from optically forbidden exciton states. Such EETs have enabled us to develop a general formula for the rate constant of EET. This is a formula in the weak-interaction limit, and so is F?rster's formula, but it correctly takes into account the above size effect.     

Time-resolved photocurrent at the MoSe2—I− photoelectrode studied with a nanosecond pulsed laser

A time-resolved transient photocurrent in the nanosecond region when illuminating the MoSe₂ — I^? semiconductorliquid junction with a pulsed laser, consists of a rapid one which immediately follows the incident light pulse and of another one with a slower decay. From the dependence of the photocurrent on light intensity, bias voltage and the effective concentration of the electrolyte, the two observed components in the spectrum were explained to originate from charge-carrier generation in the solid and electron transfer across the electrode interface, respectively.     

五甲川菁染料敏化p-NiO纳米结构电极的光电化学

研究了NiO纳米结构电极及五甲川菁染料敏化NiO纳米结构电极的光电化学行为。结果表明,NiO纳米结构电极在光照下产生阴极光电流,为p-型半导体,其禁带宽度为2.8eV,使用五甲川菁染料敏化可以显著地提高NiO纳米结构电极的阴极光电流,使NiO纳米结构电极吸收波长红移至可见光区,光电转换效率得到明显改善。研究了OTE/TiO~2/Ru(bpy)~2(SCN)~2和OTE/NiO/PMC作为光阳极和光阴极组成电池的电池特性,结果表明复合电池的光电压提高,但光电流的大小受光电流小的电极限制。     

Spontaneous vesicle formation of single chain and double chain cationic surfactant mixtures

The concentration vs composition diagram of aggregate formation of the dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB) mixture in aqueous solution at rather dilute region was constructed by analyzing the surface tension, turbidity, and electrical conductivity data and inspected by cryo-TEM images and dynamic light scattering data. Although the aqueous solution of DTAB forms only micelles, the transition from monomer to small aggregates and then to vesicle was found at 0.1 < X2 相似文献   

Novel Detection Method of Endocrine Disrupting Chemicals Utilizing Liposomes as Cell Membrane Model

Abstract

A novel detection method of endocrine disrupting chemicals (EDCs) is proposed. Liposomes encapsulating fluorescence dye was prepared as a cell membrane model and applied to detect EDCs. Leakages of dye from liposomes were observed after their exposure to EDCs. Fluorescence intensity increased significantly when the liposomes were exposed to 5 ppm EDCs. The increases showed a good correlation with EDCs' dipole moment. Therefore, polarizability is suggested as one of the factors of the liposome-EDC interaction. At lower than 5 ppm, the increases depended on EDCs' concentration. The tendency of the results was in accordance with reported estrogenic activity of EDCs.     

五甲川菁染料敏化SnO_2纳光结构多孔膜电极的光电化学研究

研究了五甲川菁敏化SnO_2纳米结构电极的光电化学行为.结合循环伏安曲线图及五甲川菁的光吸收阈值,初步确定五甲川菁染料电子基态和激发态能级位置.结果表明,五甲川菁染料电子激发态能级位置能与SnO_2纳米粒子导带边位置相匹配,因而使用该染料敏化可以显著地提高SnO_2纳米结构电极的光电流,使SnO_2纳米结构电极吸收波长红移至可见光区和近红外区,光电转换效率得到明显改善,IPCE值(单色光的转换效率)最高可达45.7％.     

Photochronocoulometric measurement of the coverage of surface-bound dyes on titanium dioxide crystal surfaces

Atomically flat terraced single-crystal anatase and rutile surfaces can be prepared allowing for the reproducible adsorption of covalently attached sensitizing dyes. Once reproducible surfaces and dye coverages are achieved, a photochronocoulometric technique is developed to measure the surface coverage of the dyes, an important parameter in determining the efficiency of sensitization. The surface-bound dyes are irreversibly oxidized by exposure to a light pulse with the n-type oxide semiconductor electrode held in depletion. A double-exponential decay of the subsequent photocurrent is then measured, where the integration of the faster decay is associated with the adsorbed dye coverage and the second much slower decay is attributed to trace regenerators, including water, in the nonaqueous electrolyte. The ruthenium-based N3 dye shows the expected linear dependence of the rate constant on light intensity whereas a dicarboxylated thiacyanine dye shows a square root dependence of its photooxidation rate on light intensity. The sublinear response of the thiacyanine dye is discussed in terms of the more complex surface chemistry that is known for this family of sensitizing dyes.     

Surprising Properties of a Furo‐Furanone

The electronic absorption, fluorescence, and excitation spectra of furo[3,4‐c]furanone ( 1 ) have been measured in different solvents at different concentrations. We observed a complex dependence of absorption and excitation spectra as a function of the concentration in CH₂Cl₂ and THF due to aggregate formation. Interestingly, the fluorescence spectra were not affected. Resolving the puzzle was made possible by the fact that 1 fits perfectly into the channels of zeolite L (ZL) microcrystals to form 1 –ZL guest–host composites. The geometry of the ZL channel system ensures a well‐defined orientation of the embedded dye molecules, thereby leading to a preferred orientation of their electronic transition dipole moment (ETDM) and thus to objects with pronounced optical anisotropy properties. This enabled us to understand that in solution the monomers that are present at low concentration form an aggregate in which the molecules sit on top of each other and arrange into a J‐type aggregate configuration at higher concentrations. The signature of the latter is observed in the 1 –ZL composites. This seems to be the first example in which the insertion of molecules into a nanochannel microcrystal has helped in understanding the weak intermolecular interactions that take place in solution.