Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

/pdf/dye-sensitized-solar-cells-50b0w2bhsr.pdf

Dye-Sensitized Solar Cells

The dye-sensitized solar cells (DSC) provides a technically and economically credible alternative concept to present day p–n junction photovoltaic devices. In contrast to the conventional systems where the semiconductor assume both the task of light absorption and charge carrier transport the two functions are separated here. Light is absorbed by a sensitizer, which is anchored to the surface of a wide band semiconductor. Charge separation takes place at the interface via photo-induced electron injection from the dye into the conduction band of the solid. Carriers are transported in the conduction band of the semiconductor to the charge collector. The use of sensitizers having a broad absorption band in conjunction with oxide films of nanocrstalline morphology permits to harvest a large fraction of sunlight. Nearly quantitative conversion of incident photon into electric current is achieved over a large spectral range extending from the UV to the near IR region. Overall solar (standard AM 1.5) to current conversion efficiencies (IPCE) over 10% have been reached. There are good prospects to produce these cells at lower cost than conventional devices. Here we present the current state of the field, discuss new concepts of the dye-sensitized nanocrystalline solar cell (DSC) including heterojunction variants and analyze the perspectives for the future development of the technology.

/pdf/dye-sensitized-solar-cells-2z7h8uxi9d.pdf

Dye-sensitized Solar Cells

The magnetoelectric effect--the induction of magnetization by means of an electric field and induction of polarization by means of a magnetic field--was first presumed to exist by Pierre Curie, and subsequently attracted a great deal of interest in the 1960s and 1970s (refs 2-4). More recently, related studies on magnetic ferroelectrics have signalled a revival of interest in this phenomenon. From a technological point of view, the mutual control of electric and magnetic properties is an attractive possibility, but the number of candidate materials is limited and the effects are typically too small to be useful in applications. Here we report the discovery of ferroelectricity in a perovskite manganite, TbMnO3, where the effect of spin frustration causes sinusoidal antiferromagnetic ordering. The modulated magnetic structure is accompanied by a magnetoelastically induced lattice modulation, and with the emergence of a spontaneous polarization. In the magnetic ferroelectric TbMnO3, we found gigantic magnetoelectric and magnetocapacitance effects, which can be attributed to switching of the electric polarization induced by magnetic fields. Frustrated spin systems therefore provide a new area to search for magnetoelectric media.

Magnetic control of ferroelectric polarization

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Organic–inorganic hybrid materials do not represent only a creative alternative to design new materials and compounds for academic research, but their improved or unusual features allow the development of innovative industrial applications. Nowadays, most of the hybrid materials that have already entered the market are synthesised and processed by using conventional soft chemistry based routes developed in the eighties. These processes are based on: a) the copolymerisation of functional organosilanes, macromonomers, and metal alkoxides, b) the encapsulation of organic components within sol–gel derived silica or metallic oxides, c) the organic functionalisation of nanofillers, nanoclays or other compounds with lamellar structures, etc. The chemical strategies (self-assembly, nanobuilding block approaches, hybrid MOF (Metal Organic Frameworks), integrative synthesis, coupled processes, bio-inspired strategies, etc.) offered nowadays by academic research allow, through an intelligent tuned coding, the development of a new vectorial chemistry, able to direct the assembling of a large variety of structurally well defined nano-objects into complex hybrid architectures hierarchically organised in terms of structure and functions. Looking to the future, there is no doubt that these new generations of hybrid materials, born from the very fruitful activities in this research field, will open a land of promising applications in many areas: optics, electronics, ionics, mechanics, energy, environment, biology, medicine for example as membranes and separation devices, functional smart coatings, fuel and solar cells, catalysts, sensors, etc.

Applications of hybrid organic–inorganic nanocomposites

The evolution of spin- and orbital-ordered states has been investigated for a series of insulating perovskites $R{\mathrm{MnO}}_{3}$ $(R=\mathrm{L}\mathrm{a},\mathrm{P}\mathrm{r},\mathrm{N}\mathrm{d},\dots{}).$ $R{\mathrm{MnO}}_{3}$ with a large ${\mathrm{GdFeO}}_{3}$-type distortion is regarded as a frustrated spin system having ferromagnetic nearest-neighbor and antiferromagnetic (AF) next-nearest-neighbor (NNN) interactions within a ${\mathrm{MnO}}_{2}$ plane. The staggered orbital order associated with the ${\mathrm{GdFeO}}_{3}$-type distortion induces the anisotropic NNN interaction, and yields unique sinusoidal and up-up-down-down AF ordered states in the distorted perovskites with ${e}_{g}^{1}$ configuration.

Distorted perovskite with e g 1 configuration as a frustrated spin system

The study of biological microstructure is one of the most important research areas in biomimicry.[1–3] Microstructure plays many important roles in living things.[2,3] For example, the charming blue color of the Morpho sulkowskyi butterfly originates from light diffraction and scattering, which results from the ordered microstructure of its scales. This form of color is usually known as structural color, which is utilized by animals both for protection and as a warning. Today, the study of structural color has been extended from biology to optics.[4–6] As well as affecting coloration, microstructure also plays an important role in self-cleaning.[2, 7] For the butterfly, the specific nanostructure enhances the hydrophobicity of its wings, which allows droplets of water to be dispersed more easily. During this process, dust particles on the surface of the wings are removed. This phenomenon is known as the “lotus effect”, which is not only very useful for natural species, but also for materials applications, such as for decoration where a natural force might be used to clean a surface. It would be interesting to discover whether it is possible to design a material that incorporates both structural color and the lotus effect, thus mimicking the wings of a butterfly. Such a material should be of great biological and technological importance. In this paper, we will show one approach to fabricating such a biomimetic decorative material by taking advantage of a nanostructured inverse opal surface. Inverse opal is a solid material that consists of a threedimensional network.[6,8–10] Orderedmonodisperse air spheres throughout the network contribute to an optical stop band, the position of which can be tuned by careful control of the periodicity of the air spheres. Colors can be observed by the naked eye when the stop band falls in the visible region. As a consequence of its unique optical properties, inverse opal has been regarded as a new-generation decorative material, in addition to its application as a photonic crystalline material.[6,11] Recently, we realized that inverse opal might also be incorporated into the design of a hydrophobic material. The solid material network of inverse opal contributes a rough surface composed of well-ordered meshes. According to the Cassie–Baxter law, the intrinsic wettability of the solid material can be greatly reduced.[12] Such a decorative material, which exhibits both structural color and the lotus effect, would be environmentally friendly and energy-efficient. For practical applications, a convenient method of fabricating a uniform inverse opal film over a large area is required. In addition, the rough inverse opal surface needs to be further optimized to imbue the surface with superhydrophobic character. We describe here the development of a dipping method that can be used to meet these criteria, and which can derive uniform inverse opal films with a nanostructured surface. The procedure for the fabrication is as follows: First, submicron-sized monodisperse polystyrene spheres and nanosized particles were ultrasonically dispersed into deionised water. A glass substrate was then immersed into the solution and withdrawn at a constant speed. It is known that a mixture of spheres with different sizes cannot be used to fabricate colloidal crystals with long-range structural order by such a deposition method,[13–15] as phase separation occurs, or an amorphous structure is formed. In our experiment, we found that this conclusion is only partially correct. A structure with long-range order can be derived when the ratio of the diameters of the spheres falls into a particular regime. Figure 1a shows an image of a structure composed of monodisperse spheres, while Figure 1b–d displays three images of structures composed of spheres of two sizes, with diameter ratios of 0.94, 0.34, and 0.07, respectively. The structure formed by the spheres of varying size depends on the diameter ratio. A structure with long-range order can be observed in films composed of monodisperse spheres, however, such order is absent in films composed of spheres of two sizes, where the diameter ratio is larger than 0.15. Usually, the particles form a structure with discernible separation when the ratio between the two types of sphere is larger than 0.5 (Figure 1b), while the domains formed by different types of particles are separated when the ratio is smaller than this value (Figure 1c). When the diameter ratio between the [7] W. P. Rothwell, W. Shen, J. H. Lunsford, J. Am. Chem. Soc. 1984, 106, 2452 – 2453. [8] Each unit cell of CHA contains 36 T sites and three cages. The HSAPO-34 used has one Si, five P, and six Al atoms per cage. [9] J. F. Haw, P. W. Goguen, T. Xu, T. W. Skloss, W. Song, Z. Wang, Angew. Chem. 1998, 110, 993 – 995; Angew. Chem. Int. Ed. 1998, 37, 948 – 949.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/anie.200390235

Structural color and the lotus effect.

A highly efficient solid-state solar cell (TiO2/dye/CuI) with improved stability was fabricated by controlling the pore filling of the porous dyed TiO2 layer with molten salt capped CuI crystals and improving the TiO2 by necking with ZnO. The molten salt controls the CuI crystal growth and acts as a protective coating for CuI nanocrystals, and necking with the more conductive ZnO improves electrical contact between TiO2 particles, both contributing to improved cell performance. Cells achieved efficiency as high as 3.8% with improved stability under continuous illumination for about 2 weeks.

Fabrication of an efficient solid-state dye-sensitized solar cell

A porous molecular crystal with guest ethanol molecules, [Mn3(HCOO)6](C2H5OH), was found to be a new type of multifunctional molecular system, which exhibits a ferroelectric transition at 165 K and a ferrimagnetic transition at 8.5 K. [Mn3(HCOO)6](C2H5OH) will give a hint to design "multiferroic" molecular materials where ferroelectric and ferromagnetic orders coexist.

Ferroelectric porous molecular crystal, [Mn3(HCOO)6](C2H5OH), exhibiting ferrimagnetic transition.

Composite materials comprised of nematic liquid crystals (LCs) and SiO2 inverse opal films were fabricated. Their optical properties were quite different from those of inverse opal films without the LCs. The optical properties could be controlled by changing the refractive indices of the LCs, which vary with orientation, phase, and temperature. In particular, the optical properties were drastically changed by thermal or photoinduced isothermal phase transitions of the LCs. This means that the photonic band structure could be controlled, and tunable photonic crystals have been achieved, based on the inverse opal structure. The mechanism of this change was investigated by the evaluation of the effective refractive indices. As a result, it was found that the change in optical properties was derived from the orientation of the LC molecules in the voids in the inverse opal film. Furthermore, once the mechanism was understood, it was also possible to control the position of the reflection peak by changing the a...

Kazuyuki Takahashi

Papers

Distorted perovskite with e g 1 configuration as a frustrated spin system

Structural color and the lotus effect.

Fabrication of an efficient solid-state dye-sensitized solar cell

Ferroelectric porous molecular crystal, [Mn3(HCOO)6](C2H5OH), exhibiting ferrimagnetic transition.

Tunable Photonic Band Gap Crystals Based on a Liquid Crystal-Infiltrated Inverse Opal Structure