Materials for photothermal solar energy conversion

Commencally or potentially available selective and non-selective absorber surfaces for solar heat collectors are reviewed and the state-of-the-art of solar collector corrosion processes is outlined. The review of available published literature has indicated that a lack of quantitative information exists, relative to corrosion of collector surfaces. Available information (mostly qualitative) on durability aspects and corrosion of solar receiver surfaces is described to indicate potential corrosion problem areas and corrosion prevention possibilities. An outline of appropriate durability tests is presented.     

Silicon nanowires for photovoltaic solar energy conversion

Semiconductor nanowires are attracting intense interest as a promising material for solar energy conversion for the new-generation photovoltaic (PV) technology. In particular, silicon nanowires (SiNWs) are under active investigation for PV applications because they offer novel approaches for solar-to-electric energy conversion leading to high-efficiency devices via simple manufacturing. This article reviews the recent developments in the utilization of SiNWs for PV applications, the relationship between SiNW-based PV device structure and performance, and the challenges to obtaining high-performance cost-effective solar cells.     

Electrochemical photovoltaic cells for solar energy conversion

Photoelectrochemical cells have attracted much more attention recently due to their feasibility as low-cost solar energy conversion devices and hence a number and variety of papers have appeared. Although some review papers have been published, no comprehensive review of electrochemical photovoltaic cells has been made. The present review is devoted to a survey of most of the dimensions of ECPV cells.Starting with photoelectrochemical processes, relevant theoretical background is presented including redox potentials, interface of the semiconductor-liquid junction and Butler-Volmer relation, etc. Much emphasis is given to the requirements of semiconductor electrodes, electrolytes, counter electrods and various cell configurations in ECPV cells. Results on photocorrosion, stability, etc. of the electrodes and the effect of temperature on the performance of the ECPV cell are discussed. Up-to-date data on various ECPV cells are presented and the current situation is discussed. In the light of this, various new materials are attractive. Finally, results on ECPV storage cells and their potential applications are discussed.     

Promising fluorescent dye for solar energy conversion based on a perylene perinone

We describe the synthesis of a dye based on a perylene perinone and evaluate its potential as the functional material for use in the luminescent solar concentrator (LSC). The dye extends the absorption wavelength of LSCs using the perylene-based dye Lumogen Red 305 by more than ~50 nm, translating into the collection of potentially 25% more photons at a reasonable fluorescent quantum yield and photostability. When the new perinone is used in a two-waveguide LSC in conjunction with Red 305, the integrated edge emission of the total LSC system may be increased more than 24% when compared to the Red 305 dye alone.     

Integrated solar capacitors for energy conversion and storage

Solar energy is one of the most popular clean energy sources and is a promising alternative to fulfill the increasing energy demands of modern society.Solar cells have long been under intensive research attention for harvesting energy from sunlight with a high power-conversion efficiency and low cost.However,the power outputs of photovoltaic devices suffer from fluctuations due to the intermittent instinct of the solar radiation.Integrating solar cells and energystorage devices as self-powering systems may solve this problem through the simultaneous storage of the electricity and manipulation of the energy output.This review summarizes the research progress in the integration of new-generation solar cells with supercapacitors,with emphasis on the structures,materials,performance,and new design features.The current challenges and future prospects are discussed with the aim of expanding research and development in this field.     

Photovoltaic and photoelectrochemical conversion of solar energy

The Sun provides approximately 100,000 terawatts to the Earth which is about 10000 times more than the present rate of the world's present energy consumption. Photovoltaic cells are being increasingly used to tap into this huge resource and will play a key role in future sustainable energy systems. So far, solid-state junction devices, usually made of silicon, crystalline or amorphous, and profiting from the experience and material availability resulting from the semiconductor industry, have dominated photovoltaic solar energy converters. These systems have by now attained a mature state serving a rapidly growing market, expected to rise to 300 GW by 2030. However, the cost of photovoltaic electricity production is still too high to be competitive with nuclear or fossil energy. Thin film photovoltaic cells made of CuInSe or CdTe are being increasingly employed along with amorphous silicon. The recently discovered cells based on mesoscopic inorganic or organic semiconductors commonly referred to as 'bulk' junctions due to their three-dimensional structure are very attractive alternatives which offer the prospect of very low cost fabrication. The prototype of this family of devices is the dye-sensitized solar cell (DSC), which accomplishes the optical absorption and the charge separation processes by the association of a sensitizer as light-absorbing material with a wide band gap semiconductor of mesoporous or nanocrystalline morphology. Research is booming also in the area of third generation photovoltaic cells where multi-junction devices and a recent breakthrough concerning multiple carrier generation in quantum dot absorbers offer promising perspectives.     

Progress and perspectives in solar energy conversion

Photovoltaic (PV) power generation can surely be considered a critical technol- ogy for overcoming global environmental problems and energy problems. This essay will review the current status and application technologies of PV power gene- ration, concluding with a discussion of the prospects of a future global-scale energy supply system based on PV power generation.     

Principles of photoelectrochemical,solar energy conversion

Photoelectrochemical devices for conversion of solar energy into both electrical energy and chemical energy are discussed with emphasis on how the various material properties of the photoactive electrodes influence device efficiency and stability. The similarity between photoelectrochemical cells (PECs) and solid state devices is used to model their behaviour and optimize such parameters as band gap, doping level, minority carrier lifetime, etc. A model is presented which calculates the electron affinity of any semiconductor and allows the prediction of the open circuit voltage of wet photovoltaic cells and optimum biasing forchemical producing cells. The effects of absorbed ions at the semiconductor/electrolyte interface are reviewed. The temperature dependence of the energy levels in the semiconductor and the electrolyte are considered and the implications of these results to operation of PECs at elevated temperature are discussed. The major differences between PECs and solid state devices are the stability considerations. The thermodynamics of this problem is discussed. Other important degradation mechanisms and some solutions to these problems are reviewed. Finally, a prognosis of the future of this field is presented.     

Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy

Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.     

Chemical vapor deposition of thin semiconductor films for solar energy conversion

The surfaces intercepting the incident radiation in solar energy converters must have a spectral profile that is properly matched to the solar emission and thermal reradiation properties, they must withstand high temperatures without harmful changes of their optoelectronic characteristics and they must operate for long enough to be economically viable. Multilayer systems deposited by chemical vapor deposition offer attractive features. The paper reviews methods of preparation and the optical performance of thin semiconductor films deposited from the vapor phase that meet all three requirements, in particular for applications at temperatures of 500°C. If developed further, chemical vapor deposition will be particularly well adapted to the requirements imposed on the thin semiconductor films used in photothermal converters.     

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.     

Highly efficient nanostructured metal-decorated hybrid semiconductors for solar conversion of CO2 with almost complete CO selectivity

Photocatalytic reduction of CO₂ into solar fuels is regarded as a promising method to address global warming and energy crisis problems. Although heterostructured hybrid metal oxide catalysts have been used for CO₂ reduction, selective control for CO production-only remains the subject of debate. In this paper, we report an absolute selectivity for CO production-only with enhanced photocatalytic ability using Ag-decorated reduced titanium oxide/tungsten hybrid nanoparticles (blue TiO₂/WO₃–Ag HNPs) at 1166.72 μmol g⁻¹ h⁻¹ with an apparent quantum yield of 34.8%. The construction of a Z-scheme between blue TiO₂ and WO₃ domains with an excellent band alignment provided remarkably improved separation of photoinduced charges. Importantly, the presence of novel Ag not only produces the highest selectivity up to 100% CO production-only, but also increases the photocatalytic electron reaction rate (2333.44 μmol g⁻¹ h⁻¹).     

光催化太阳能转换及环境净化材料的现状和发展趋势

21世纪人类面临的最大课题是能源和环境问题,利用太阳能来解决全球性的能源和环境问题越来越受到人们的重视,各种技术手段应运而生.最近,我们成功地利用可见光响应的半导体光催化材料来分解水和降解有机污染物,实验中还发现如果光催化材料具有合适的能带结构,其光催化的效果就越显著.本文简要评述了光催化材料在太阳能转化和环境净化方面应用的研究背景、现状和发展趋势.     

Monitoring of concentrated radiation beam for photovoltaic and thermal solar energy conversion applications

Methods for evaluating the light intensity distribution on receivers of concentrated solar radiation systems are described. They are based on the use of Lambertian diffusers in place of the illuminated receiver and on the acquisition of the scattered light, in reflection or transmission mode, by a CCD camera. The spatial distribution of intensity radiation is then numerically derived from the recorded images via a proprietary code. The details of the method are presented and a short survey of the main applications of the method in the photovoltaic and thermal solar energy conversion field is proposed. Methods for investigating the Lambertian character of commercial diffusers are also discussed.     

Influence of surface treatments on CdSe thin films in photoelectro-chemical solar energy conversion

Photovoltaic performance of semiconductor-liquid junction solar cell using electro-codeposited thin filmn-CdSe is found to improve significantly by proper surface treatments. The solid state parameters of annealed films are calculated and compared with those of unannealed film-based cells. Chemical etching is found to improve short circuit current and fill factor whereas photoelectrochemical etching technique improves the stability of photoanode in polysulphide electrolyte. Annealing promotes incipient fusion of small crystallites, thus reducing the grain boundaries which are known to act as recombination centres for minority carriers and trapping centre for majority carriers. The conversion efficiency and stability are found to improve by chemical etching of the semiconductor layer because chemical etching pins Fermi level of CdSe photoanode and promotes exchange current density.