Extremely thin absorber solar cells based on nanostructured semiconductors

Abstract

Extremely thin absorber (eta) solar cells aim to combine the advantages of using very thin, easily and cheaply produced absorber layers on nanostructured substrates with the stability of all-solid-state solar cells using inorganic absorber layers. The concept of using nanostructured substrates originated from the dye-sensitised solar cell, where having a very high surface area allows the use of very thin layers of dye while still absorbing sufficient sunlight. However, both the dye and liquid electrolyte used in these devices demonstrated poor stability, and efforts were made to replace them with very thin inorganic absorber layers and solid state hole collectors respectively. The combination of these concepts – a nanostructured substrate coated with a very thin inorganic absorber and completed with a solid state hole collector – is known as an eta solar cell. This review summarises the development of both the inorganic absorbers and solid state hole collectors in porous TiO₂ and ZnO nanorod based cells, focusing on the material properties and growth/deposition methods. Future possibilities for eta solar cells are discussed, including utilisation of a wider range of materials, synthesis methods and novel materials such as quantum dots to produce tuned band gap and multijunction solar cells.     

On the transformation textures influenced by deformation in electrical steels,high manganese steels and pure titanium sheets

Transformation texture is normally different to deformation and recrystallization textures, thus influencing materials properties differently. As deformation and recrystallization are often inseparable to transformation in materials which shows a variety in types such as diffusional or non-diffusional transformations, different phenomena or rules of strengthening transformation textures occur. This paper summarizes the complicated phenomena and rules by comparison of a lot of authors’ published and unpublished data collected from mainly electrical steels, high manganese steels and pure titanium sheets. Three kinds of influencing deformation are identified, namely the dynamic transformation with concurrent deformation and transformation, the transformation preceded by deformation and recrystallization and the surface effect induced transformation, and the textures related with them develop in different mechanisms. It is stressed that surface effect induced transformation is particularly effective to enhance transformation texture. It is also shown that the materials properties are also improved by controlled transformation textures, in particular in electrical steels. It is hoped that these phenomena and processing techniques are beneficial to the establishment of transformation texture theory and property improvement in practice.     

Advanced triboelectric materials for liquid energy harvesting and emerging application

Triboelectric properties of materials play an essential role in liquid energy harvesting and emerging application. The triboelectric properties of materials can be controlled by chemical functionalization strategy, which can improve the utilization of liquid energy resources or reduce the hazards of electrostatic effects. Herein, the latest research progress in molecular modification based on chemical functionalization to control triboelectric properties of materials is systematically summarized. By introducing the mechanism of contact electrification between liquid and solid materials and the developmental history of liquid–solid contact electrification, the influence of solid surface charge density, wettability and liquid properties on contact electrification of liquid and solid materials is described. Research progress on chemical functionalization for improving the hydrophobicity of solid materials, surface charge density of solid materials and triboelectric properties of liquid materials is highlighted. The focus then turns to the significance of enhanced liquid–solid contact electrification in energy harvesting, self-powered sensors and metal corrosion protection. Recent advances in chemical functionalization strategies for weakening the triboelectric properties of solid and liquid materials are also highlighted. Finally, an outlook of the potential challenges for developing chemical functionalization strategies in the field of solid surface modification and liquid molecular modification is presented.     

Characterization of saturated porous bodies

Measurement of the response of a saturated body to mechanical and thermal strains can be used to determine the permeability and viscoelastic properties of the body. For example, bending a saturated beam creates a pressure gradient in the pores, and as the liquid flows to equilibrate the pressure, the force required to sustain a fixed deflection decreases. Analysis of the kinetics of force relaxation yields the permeability, in addition to the elastic modulus of the body; if viscoelastic relaxation of the solid phase occurs, it can also be measured. This method permits measurement of very low permeabilities in minutes or hours, but it is useful only for structurally homogeneous materials (such as cement paste) that can be formed into slender beams. For concrete, it is more practical to find the permeability by analysis of thermal expansion kinetics. When a saturated body is heated, the liquid expands more than the solid, and the expansion of the liquid stretches the solid network like a spring; consequently, the apparent thermal expansion coefficient is high. During an isothermal hold, the solid phase squeezes the liquid out of the pores and the body contracts. Analysis of the kinetics of thermal dilatation yields the permeability of the body. Recent experiments reveal an anomalously high thermal expansion coefficient for the water confined in the small pores of cement paste.     

Effect of particle morphology on mechanical properties of liquid marbles

In order to better understand the influence of the shape of solid particles on the stability of liquid marbles, we investigated liquid marbles stabilized by hydrophobized calcium carbonate particles with spherical and rod-shaped morphologies. Static properties, such as the effective surface tension, and the dynamic behavior i.e. the compression-decompression features for several cycles of the liquid marbles were investigated. Liquid marbles stabilized with spherical CaCO₃ particles show an elastic response to mechanical deformation almost up to collapse. In contrast, liquid marbles prepared with rod-like particles exhibit a more plastic response to compression. It is concluded that the main differences in behavior of the prepared liquid marbles arise from how the solid particles can arrange/orient at the air/water interface.     

The study of the kinetics of water spreading on solid phases of carbon allotropic materials

Kinetics of water spreading on the surface of solid phases of various carbon materials has been first studied with the use of high-speed video filming (up to 1200 frames per second). It has been found that rates of low-temperature liquid and metal melts spreading and wetting the surface of solid phases are close in time (the process length is 10⁻²–10⁻³s) and in both the cases the spreading occurs in an inert mode. It has been shown that at the final stages the spreading of low-temperature liquids occurs at a viscous mode (10–30 min) caused by the presence of an adsorbed layer (coat) on the solid phase surface due to the environment.     

Ultrafast growth of single-crystalline Si nanowires

Silicon nanowires (SiNWs) have been catalytically synthesized by heat treatment of Si nanopowder at 980 °C. The SiNWs comprise crystalline Si nanoparticles interconnected with metal catalyst. The formation mechanism of nanowires generally depends on the presence of Fe catalysts in the synthesis process of solid–liquid–solid (SLS). Although gas phase of vapor–liquid–solid (VLS) method can be used to produce various of different nanowire materials, growth model based on the SLS mechanism by heat treatment is more ascendant for providing ultrafast growth of single-crystalline Si nanowires and controlling the diameter of them easily. The growth of single-crystalline SiNWs and morphology were discussed.     

Laser ablation in liquids: Applications in the synthesis of nanocrystals

This work presents a survey on the recent progress in laser ablation of a solid target in a confining liquid for the synthesis of nanocrystals with focus on the mechanism of nanocrystal growth. The effects of liquid confinement, thermodynamic nucleation, phase transition, and kinetic growth of the nanostructures are discussed in detail. Besides, a variety of applications of the laser ablation is reviewed, including surface patterning, surface cleaning, and surface coating. Experimental results and theoretical analysis indicate that laser ablation of a solid target in a confining liquid provides an effective means to synthesize nanocrystals, especially for the metastable nanocrystals such as diamond and carbon related materials, immiscible alloys, etc. The laser ablation in liquids has demonstrated the following advantages: (i) a chemically “simple and clean” synthesis, (ii) an ambient conditions not extreme temperature and pressure, and (iii) the new phase formation of nanocrystals may involve in both liquid and solid. These advantages allow us to combine selected solid targets and liquid to fabricate compound nanostructures with desired functions.     

Bioinspired Solid Organogel Materials with a Regenerable Sacrificial Alkane Surface Layer

In nature, lifetime‐long functionalities of land plant leaves rely on the regenerability as well as the solid feature of the epicuticular wax layer. Inspired by the regenerable solid epicuticular wax on land plant leaf surfaces, herein a type of solid organogel material with regenerable sacrificial alkane surface layer is reported. This type of surface material is demonstrated to be of great practical importance for tackling solid deposition, such as anti‐icing, antigraffiti, and antifouling, since the deposited foreign materials can be easily removed together with the alkane surface layer. Significantly, the solid alkane layer does not contaminate nearby surfaces due to its solid nature in both working and stand‐by conditions, which is completely different to liquid‐infused materials.     

Crystalline quality of the trigonal piezoelectric materials and effects of the extended defects

Many frequently used or promising piezoelectric materials belong to crystal classes 32 or 3m. Among them are α quartz and its crystallographic analogs (AlPO(4), GaPO(4), α-GeO(2), etc.), the numerous materials of the langasite (La-(3)Ga(5)SiO,sub>14) family and also lithium tantalate (LiTaO,sub>3) and lithium niobate (LiNbO 3). In this paper we study the present state of the art for these materials, indicate their principal point and extended defects, and present methods to reduce the dislocation density. Large concentrations of intrinsic point defects often exist in crystal grown at very high temperatures. The point defects (intrinsic or related to impurities) modify the constants and can increase the acoustic losses. This is the case for the alkali ions and the OH that induce severe losses in different temperature intervals. The extended defects also affect the performances of the piezoelectric devices. Some, such as twins, ferroelectric domains, or large solid or liquid inclusions, have very detrimental effects. Dislocations, growth bands, and planar defects are more difficult to avoid and affect the devices in a more subtle manner. In quartz and its analogs, dislocations seem to increase the nonlinear elastic effects and have a collective effect on the vibration modes, particularly in energy trapping resonators. Growth bands and stacking faults also produce similar effects.     

Simulation of capillary shrinkage cracking in cement-like materials

In drying suspensions, water loss leads to a capillary pressure build-up in the liquid phase. This effect may also be observed in fresh cement-based materials subjected to evaporation at an open surface. If under decreasing water content the near-surface solid particles are no longer covered by a plane water film, menisci develop along with an associated build-up of negative capillary pressure, resulting in shrinkage and possibly in cracking. A 2D model for simulating the described physical process is presented. For arranging the particles in the 2D specimen a stochastic–heuristic algorithm is used. Subsequently, the course of the water front between the particles is calculated by assuming a constant curvature of the water surface. Particle mobility is taken into account by adopting interparticle forces and performing equilibrium iterations. The model allows one to study the influences of the particle size distribution as well as of the properties of the liquid phase on the capillary pressure build-up and on the cracking risk.     

Spinning Liquid Metal Droplets on Ice

The non-contact and non-wetting droplet motion isolated from the solid surface has a high degree of freedom and thus can exhibit many peculiar interfacial phenomena. Here, an experimental phenomenon of spinning liquid metal droplets on an ice block is discovered, which adopts the dual solid-liquid phase transition of the liquid metal and the ice. The whole system is somewhat a variant of the classic Leidenfrost effect, which directly uses the latent heat released by the spontaneous solidification of the liquid metal droplet as a heat source to melt the ice and create an intervening lubricant water film. Interestingly, it is found that the droplets on ice become very mobile and undergo rapid spin as the solidification process proceeds. A series of comparative experiments clarify that the circumferential driving force comes from the escaping bubbles as the ice melts. Furthermore, by comparing the motion characteristics of different kinds of liquid metal droplets and solid balls on ice and investigating their physical properties and heat transfer, it is disclosed that the spin effect can be universal for objects of different materials, as long as the two necessary elements of rapid liquid film establishment and gas bubble release can be satisfied simultaneously.     

The thermophysical characteristics of the surfaces of crystalline bodies

Up to now, with very few exceptions, no distinction has been made in the scientific literature on the physics of interphase phenomena between the notions on surface energy and surface tension. For the liquid state, this is unimportant; however, for the solid crystalline state, the situation changes significantly. As follows from the results of calculations in [1–3], the ratio of the surface tension to the surface energy, for example, for alkali halide crystals at absolute zero temperature, varies from five to ten. It is very difficult to experimentally check these results because of lack of reliable methods for measuring these quantities in the solid state; furthermore, it is impossible to ascertain which method should be applied to measure one or another quantity. The main force characteristic of the surface of crystalline bodies, namely, the tensor of surface tension, is determined. The most general relationship between the components of the surface tension tensor and the surface energy is derived for a multicomponent solid, from which, with quite definite (but not always trivial) assumptions, the relation between them (known in the literature) is obtained. A mechanism is suggested to explain the considerable difference between the numerical values of the surface energy and the surface tension in the solid state.     

In situ imaging of multiphase bio-interfaces at the micro-/nanoscale

The multiphase bio-interfacial system constituted by biological surfaces and their surrounding environment is usually considered to be an essential clue for exploring the mysterious relationship between surface architecture and function. As a visualizing method to understand these systems, in situ imaging of multiphase interfaces (e.g., air/liquid/solid and oil/water/solid systems) at the micro-/nanoscale, still remains a huge challenge, as a result of their heterogeneity and complexity. Here, recent progress on real-space micro-/nanoscale imaging of multiphase bio-interfacial systems is reviewed; this includes several techniques and imaging results on bio-interfaces, such as the lotus leaf, fish scale, living cell's surface, and fresh tissue surface. The results evidently show that interfacial structures have a significant impact on the state of the microscopic multiphase interface, further influencing specific functions. Based on this research, technical innovations, some more complicated multiphase interface systems, and structure-function coupling mechanism are proposed.     

Adapting Shot Peening for Surface Texturing Using Customized Additive Manufactured Shots

Surface textures in engineering materials not only affect the reflective properties and aesthetics but if properly designed can modulate surface-related properties such as wettability, fatigue, wear, corrosion, and scratch resistance. Herein, a new surface texturing method is introduced based on the conventional shot peening process. Custom shots are designed, and their surface texturing capability is investigated on acrylonitrile butadiene styrene (ABS) polymer substrates. A finite-element model is developed to bombard the substrate using AISI 316 stainless steel customized shots. The generated unique textures are compared qualitatively by visual examination and quantitatively using the standard surface roughness parameters. As a proof of concept, preliminary experiments are performed using a candidate custom shot and a spherical shot to treat the ABS sheets. The results highlight the high potential of the shot peening technique paired with additive manufacturing for customizing the peening media to be used for surface texturing polymeric materials.     

Absorption removal of carbon dioxide in the presence of inert solid particles (flour powder)

Abstract

An experimental analysis of the absorption removal of carbon dioxide with the presence of inert solid particles on the surface of the absorbent liquid is presented. A batch absorber with quiescent absorbent liquid has been applied to study the absorption removal of carbon dioxide by water in the isothermal system. The flour powder is introduced as the inert solid particles in the carbon dioxide absorption system. Tests with the flour powder in water are examined. The mass fluxes of carbon dioxide for the cases with and without the flour powder are then compared to elucidate the effects of inert solid particles on isothermal gas absorption. The results indicate a significant difference between these two cases for the concentrations of the flour powder in the absorbent liquid (WF) being in the range of experimental conditions, namely 0.001 to 0.03 g flour in 10 ml liquid. In general, the inert solid particles of the flour powder as the impurities in water with WF in the range of this study tend to decrease the carbon dioxide absorption rates for the experimental absorption system under investigation. Thus, various concentrations of inert solid particles cause various levels of surface resistance and affect the gas absorption rates. This kind of information is very useful for the gaseous pollutants removal that the impurities of inert solid particles contaminate the isothermal gas absorption system, and for the absorption removal of carbon dioxide associated with the control of the green house effect.     

Analysis of the formed track in solid state materials using atomic force microscopy

The track formation in solid state materials, from the theoretical point of view, is still under study. One way to understand the track formation mechanisms and radiation damage of the charged particles in some materials such as polymers, glasses and minerals, is to analyse the surface topography effects. In this work, the track formation analysis in polycarbonate material is presented using an atomic force microscope (AFM) to characterise the evolution of the track on the material surface and beyond a thin layer of the surface material. The AFM is very useful to obtain valuable information at the level of the atomic structure of the materials and of the nuclear tracks, due to its high resolution and very easy operation involving also a simple sample preparation. The results show the development of the formed track by means of induced surface effects after being exposed to ionising radiation and chemical etching.     

Transparent superhydrophobic surfaces for applications of controlled reflectance

This work involves a new optical application for transparent superhydrophobic materials, which enables low-energy optical contact between a liquid and solid surface. The new technique described here uses this surface property to control the reflectance of a surface using frustration of total internal reflection. Surface chemistry and appropriate micro-scale and nano-scale geometries are combined to produce interfaces with low adhesion to water and the degree to which incident light is reflected at this interface is controlled by the movement of water, thereby modifying the optical characteristics at the interface. The low adhesion of water to superhydrophobic surfaces is particularly advantageous in imaging applications where power use must be minimized. This paper describes the general approach, as well as a proof-of-principle experiment in which the reflectance was controlled by moving a water drop into and out of contact with a superhydrophobic surface by variation of applied electrostatic pressure.     

Bonding Surface area and Bonding Mechanism-Two Important Factors fir the Understanding of Powder Comparability

Abstract

Two factors could be regarded as primary factors for the compactability of powders: the dominating bond mechanism and the surface area over which these bonds are active. Owing to considerable experimental difficulties, these factors have not been evaluated in any detail for pharmaceutical materials. Instead, more indirect, secondary factors are normally studied and used for correlations with tablet strength. Such secondary factors are particle size, shape and surface texture. Also the importance of volume reduction mechanisms, i.e. elastic deformation, plastic deformation and particle fragmentation have been studied in detail.

For the investigation of dominating bond mechanisms and estimation of the magnitude of the surface area of the solids involved in interparticulate attraction in compacts several pharmaceutical excipients representing both plastically deforming materials (sodium chloride, Avicel® PH 101, Sta-Rx 1500®, and sodium bicarbonate) and fragmenting materials (lactose, sucrose, paracetamol and Emcompress®) have been used in a series of publications from our laboratory.

The bonding mechanisms discussed have been solid bridges, representing continous solid bridges between tablet particles, intermolecular forces, representing weaker attraction forces active over distances and mechanical interlocking, representing a bond type dependent on hooking and twisting of irregularly shaped particles. To characterize the dominating bond mechanisms, measurements of compact strength has been performed in media known to reduce bonding with intermolecular forces. The media used were liquids with different dielectric constants and films of magnesium stearate. The results establish that the intermolecular forces constitute the dominating bond mechanism for pharmaceutical materials. Bonding with solid bridges contribute to the compact strength only for coarse plastically deforming materials that can melt during compaction. Only for sodium chloride, of the materials tested, is there substantial evidence for the existence of solid bridges. Bonding with mechanical interlocking is a bonding mechanism of minor importance for most of the investigated materials with the possible exception of Avicel® PH 101.

The results indicate that the surface area utilized for bonding with solid bridges for sodium chloride as measured with gas adsorption is small in relation to the total surface area of the compact. For all the materials bonding with intermolecular forces, only a proportional relation between compact surface area and bonding surface area could be possible. By using permeametry surface area data, the surface specific compact strength was characterized and found similar for all materials bonding primarily with intermolecular forces. For such materials a large bonding surface area will thus be obtained if the surface area of the particles in the tablet is large. This could either be achieved by the use of materials that undergo extensive fragmentation or by the use of very fine paniculate materials or qualities with pronounced surface roughness. It is suggested that most of the so called plastically deforming pharmaceutical materials often possess inadequate plasticity for the development of large zones that could take part in the interparticulate attraction by intermolecular forces.     

Transport and fate of volatile organic chemicals in unsaturated, nonisothermal, salty porous media: 1. Theoretical development.

A wide variety of volatile organic chemicals (VOC) have been applied to agricultural land or buried in chemical waste sites. The fate of these chemicals depends upon several mechanisms such as sorption, degradation, and transport in liquid and gaseous phases. Understanding the transport mechanisms affecting the volatile chemicals can lead to better management strategies. A theory describing inorganic solute transport, water and heat transfer, and the fate and transport of VOC in porous media has been developed. This theory includes matric water pressure head, solution osmotic pressure head, gravity pressure head, temperature, inorganic solute concentration, and VOC concentration gradients as driving forces for heat and mass transfer. The effect of surface tension, as a function of VOC concentration and temperature, on the matric water pressure head is included. The VOC can be associated with gas, liquid, and solid phases of the porous media. The gas and liquid phases are mobile, but the solid phase is immobile. The transfer of VOC across the gas/liquid, liquid/solid, and gas/solid interfaces is included using sorption-equilibrium assumptions at the interfaces. The VOC can degrade. This degradation is described by a first-order decay rate. The theory can be used to predict spatial and temporal variations of water content, temperature, inorganic concentration and the total concentration of VOC within a porous medium. The concentration of VOC in each phase can be predicted also.