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 ...

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Dye-Sensitized Solar Cells

Organic solar cell research has developed during the past 30 years, but especially in the last decade it has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. This was achieved by the introduction of new materials, improved materials engineering, and more sophisticated device structures. Today, solar power conversion efficiencies in excess of 3% have been accomplished with several device concepts. Though efficiencies of these thin-film organicdevices have not yet reached those of their inorganic counterparts (η ≈ 10–20%); the perspective of cheap production (employing, e.g., roll-to-roll processes) drives the development of organic photovoltaic devices further in a dynamic way. The two competitive production techniques used today are either wet solution processing or dry thermal evaporation of the organic constituents. The field of organic solar cells profited well from the development of light-emitting diodes based on similar technologies, which have entered the market recently. We review here the current status of the field of organic solar cells and discuss different production technologies as well as study the important parameters to improve their performance.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400094498

Organic solar cells: An overview

Leu-M

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

A review of Ga2O3 materials, processing, and devices

Photo- and Electrochromism of Polyoxometalates and Related Materials

Positive temperature coefficient of resistivity (PTCR) materials have become very important components, and among these materials barium titanate compounds make up the most important group. When properly processed these compounds show a high PTCR at the Curie temperature (the transition temperature from the ferroelectric tetragonal phase to the paraelectric cube phase). In the first half of this paper literature related to the resistivity-temperature behaviour is discussed. As explained by the well established Heywang model, the PTCR effect is caused by trapped electrons at the grain boundaries. From reviewing experimental results in the literature it is clear that the PTCR effect can not be explained by assuming only one kind of electron trap. It is concluded that as well as barium vacancies, adsorbed oxygen as 3d-elements can act as electron traps. In the second half of this paper, the influence of the processing parameters on the PTCR related properties is discussed. Special emphasis is placed on the phenomenon that the conductivity and grain size decrease abruptly with increasing donor concentration above ∼ 0.3 at%. Several models explaining this phenomenon are discussed and apparent discrepancies in experimental data are explained.

The positive temperature coefficient of resistivity in barium titanate

Dye Sensitization and Surface Structures of Semiconductor Electrodes

Hydrothermal synthesis of fine zinc oxide particles under supercritical conditions

Near-infrared reflection from periodically aluminium-doped zinc oxide thin films

A systematic study of the solubility of PbO in the ( Bi 1− x Pb x ) 2 Sr 2 CaCu 2 O 8+ y compound at various oxygen partial pressures has been carried out. The solubility was found to increase as the oxygen partial pressure decreased. The change in lattice parameter with PbO concentration supported the solubility data. By annealing the 2212 phase with a large amount of PbO under a high oxygen partial pressure, a secondary phase having an XRD pattern similar to that of Ca 2 PbO 4 was precipitated. Simultaneously, the 2212 phase transformed from a monoclinic (nearly orthorhombic) to a tetragonal structure in the 2212 phase with a small amount of PbO. The annealing effect in the (Bi, Pb)-based superconductor can be explained by the variation of the solubility of PbO due to the oxidation of the Pb 2+ ions, when the secondary phase is assumed to be isostructural with Ca 2 PbO 4 .

Masasuke Takata

Papers

The positive temperature coefficient of resistivity in barium titanate

Dye Sensitization and Surface Structures of Semiconductor Electrodes

Hydrothermal synthesis of fine zinc oxide particles under supercritical conditions

Near-infrared reflection from periodically aluminium-doped zinc oxide thin films

Influence of the oxygen partial pressure on the solubility of PbO in the (Bi, Pb)2Sr2CaCu2O8+y superconducting oxides