光电化学电极的研究及其在太阳能转化方面的应用

TiO2半导体光电极的发现引发了科学界大量关于半导体光电极的研究.目前,对TiO2的掺杂,对新材料的探索以及对异质结的深入研究,目的都是为了提高半导体光电极的太阳光利用效率.敏化太阳能电池的出现是半导体光电极在实用化方面迈进的一大步.文章简述半导体光电极的研究历史,并对该领域将来的研究方向进行了展望.     

光电化学电极的研究及其在太阳能转化方面的应用

TiO2半导体光电极的发现引发了科学界大量关于半导体光电极的研究.目前,对TiO2的掺杂,对新材料的探索以及对异质结的深入研究,目的都是为了提高半导体光电极的太阳光利用效率.敏化太阳能电池的出现是半导体光电极在实用化方面迈进的一大步.文章简述半导体光电极的研究历史,并对该领域将来的研究方向进行了展望。     

Production and Storage of Energy with One-Dimensional Semiconductor Nanostructures

This article outlines state-of-the-art energy technologies, including production and storage, available to us through semiconductor nanomaterials. The nanostructure growth processes have been illustrated in detail, with emphasis on the latest developments in hierarchical and radial-composition modulated nanostructures. On the energy efficiency and generation part, light-emitting diodes, photovoltaics, photoelectrochemistry, thermoelectric, and fuel cells have been discussed. In the energy storage part, supercapacitors and lithium batteries have been discussed.     

Novel method for photovoltaic energy conversion using surface acoustic waves in piezoelectric semiconductors

This paper presents a novel principle for photovoltaic (PV) energy conversion using surface acoustic waves (SAWs) in piezoelectric semiconductors. A SAW produces a periodically modulated electric potential, which spatially segregates photoexcited electrons and holes to the maxima and minima of the SAW potential. The moving SAW collectively transports the carriers with the speed of sound to the electrodes made of different materials, which extract electrons and holes separately and generate dc output. The proposed active design is expected to have higher efficiency than passive designs of the existing PV devices and to produce enough energy to sustain the SAW.     

Modifying optical properties of ZnO nanowires via strain-gradient

We conduct systematical cathodolumiuescence study on red-shift of near-band-edge emission energy in elastic bent ZnO nanowires with diameters within the exciton diffusion length （- 200 nm） in liquid nitrogen temperature （81 K）. By charactering the emission spectra of the nanowires with different; local curvatures, we find a linear relationship between strain-gradient and the red-shift of near-band-edge emission photon energy, an elastic strain-gradient effect in semiconductor similar to the famous flexoelectric effect in liquid crystals. Our results provide a new route to understand the inhomogeneous strain effect on the energy bands and optical properties of semiconductors and should be useful for designing advanced nano-optoelectronic devices.     

聚光光伏与温差联合发电装置的研究

针对太阳能量利用率较低的现状,设计了基于砷化镓多结太阳能电池、半导体温差发电片的聚光光伏与温差联合发电装置.通过测量得出单独聚光光伏发电模块在几何聚光比为75时光电转换效率最大,达31.87%;而在加了半导体温差发电模块之后在几何聚光比为112时系统光电转换效率达32.81%,提高了整体光能量转化电能效率.     

High-efficient Schottky-junction silicon solar cell using silver nanowires covering nitrogen-doped amorphous carbon

Synthesized graphene (Gr) on metal substrates that requires additional surface-to-surface transfer procedure to form Gr-on-silicon (Gr-Si) Schottky-junction configuration, which in turn results in the photovoltaic degradation caused by both mechanical damages and chemical contaminations during several wet chemical steps. This current issue has motivated us to develop alternative Schottky-junction configuration using silver nanowires (AgNWs) covering nitrogen (N)-doped amorphous carbon (a-C) films annealed in the temperature range 750–900 °C. Compared to the Schottky-junction Si solar cell based on 900 °C annealed N-doped a-C films (C_N-900-Si) with only Ag grid, all of AgNWs-C_N-900-Si solar cells exhibit the significant enhancement of photovoltaic characteristics. Consequently, the remarkable power conversion efficiency (PCE) of 6.17% is achieved on 0.2 wt% AgNWs-C_N-900-Si solar cell, which is far superior to that of the C_N-900-Si solar cell with only Ag grid (~0.13%). Furthermore, the 0.2 wt% AgNWs-C_N-900-SiNWs solar cell shows the highest short-circuit current density (J_SC) of 23.42 mA/cm² and PCE of 7.67%, which is a PCE enhancement of ~24% when compared to the 0.2 wt% AgNWs-C_N-900-Si solar cell. This study demonstrates that AgNWs network can accelerate the charge carrier extraction from Schottky-contact between C_N-900 and n-Si substrate, leading to greatly reduced series resistance that results in significantly enhanced photovoltaic characteristics.     

On the thermodynamic limit of photovoltaic energy conversion

An infinite stack ofp—n junctions with smoothly varying bandgap from ∞ to 0 is considered. AnI —V characteristic is derived, which is more correct than the classical exponential characteristic. It is shown that open-circuit operation is a reversible process and leads to the Carnot efficiency, if one defines the efficiency in the way that is usual in the theory of thermodynamic engines. If instead one uses the definition of efficiency usual in photovoltaics, open-circuit mode gives rise to zero efficiency. Then operation at maximum efficiency equals operation at maximum power and is not reversible.     

Insertion of fullerene layer for bulk heterojunction organic photovoltaic cell fabricated by electrospray deposition method

An improved power conversion efficiency (PCE) of bulk heterojunction organic photovoltaic cell (OPV) was achieved by inserting an n‐type [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) layer between the active layer and a metal electrode. The controlled substrate temperature was found to be a useful parameter for the multilayer structure (active layer/ PCBM) by the electrospray deposition method. Under optimized substrate temperature during the PCBM deposition, a multilayer structure could be formed, and the PCE was improved up to 1.94%.

     

Hierarchical nanowires for high-performance electrochemical energy storage

Nanowires are promising candidates for energy storage devices such as lithium-ion batteries, su- per（：apa.citors and lithium-air batteries. However, simple-structured nanowires have some limitations hence the strategies to make improvements need to be explored and investigated. Hierarchical nanowires with enhanced periormanee have been considered as an ideal candidate for energy storage due to the novel structures and/or synergistic properties. This review describes some of the recent progresses in the hierarchical nanowire merits, classification, synthesis and performance in energy storage applieat, ions. Herein we discuss the hierarchical nanowires based on their structural design from three major categories, including exterior design, interior design and aligned nanowire assembly. This review also briefly outlines the prospects of hierarchical nanowires in morphology control, property enhancement and application versatility.     

Metallic nanowires for subwavelength waveguiding and nanophotonic devices

Plasmonics is a rapidly developing field concerning light manipulation at the nanoscale with many potential applications, of which plasmonic circuits are promising for future information technology. Plasmonic waveguides are fundamental elements for constructing plasmonic integrated circuits. Among the proposed different plasmonic waveguides, metallic nanowires have drawn much attention due to the highly confined electromagnetic waves and relatively low propagation loss. Here we review the recent research progress in the waveguiding characteristics of metallic nanowires and nanowire-based nanophotonic devices. Plasmon modes of both cylindrical and pentagonal metallic nanowires with and without substrate are discussed. Typical methods for exciting and detecting the plasmons in metallic nanowires are briefly summarized. Because of the multimode characteristic, the plasmon propagation and emission in the nanowire have many unique properties, benefiting the design of plasmonic devices. A few nanowire-based devices are highlighted, including quarter-wave plate, Fabry-Prot resonator, router and logic gates.     

Rational design of photoelectrodes for photoelectrochemical water splitting and CO2 reduction

Solar energy has promising potential for building sustainable society. Conversion of solar energy into solar fuels plays a crucial role in overcoming the intermittent nature of the renewable energy source. A photoelectrochemical (PEC) cell that employs semiconductor as photoelectrode to split water into hydrogen or fixing carbon dioxide (CO₂) into hydrocarbon fuels provides great potential to achieve zero-carbon-emission society. A proper design of these semiconductor photoelectrodes thus directly influences the performance of the PEC cell. In this review, we investigate the strategies that have been put towards the design of efficient photoelectrodes for PEC water splitting and CO₂ reduction in recent years and provide some future design directions toward next-generation PEC cells for water splitting and CO₂ reduction.     

Sustainability and renewable energies – a critical look at photovoltaics

The current status of photovoltaic modules from wafer‐based Si and thin films of Si, CuInGaSe₂ (CIGS), CdTe and III–V compound semiconductors in terms of efficiencies and market volumes is shortly summarized and evaluated with respect to sustainability. We discuss the critical raw materials such as gallium, indium and germanium. These materials are either incorporated into the absorber layers or used as substrate materials, i.e. Ge in the case of III–V semiconductor based cells. On a 100 GW per year production level the availability of indium and tellurium will limit the growth of the respective photovoltaic technology. Alternative materials are on the horizon, such as the kesterite‐type materials which offer the possibility to replace In and Ga in CuInGaSe₂, but it may take a long period of time for modules of these materials to reach the production‐level efficiencies of today's established technologies. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Semiconductor nanowires for novel one-dimensional devices

Low-dimensional semiconductors offer interesting physical phenomena but also the possibility to realize novel types of devices based on, for instance, 1D structures. By using traditional top-down fabrication methods the performance of devices is often limited by the quality of the processed device structures. In many cases damage makes ultra-small devices unusable. In this work we present a recently developed method for bottom-up fabrication of epitaxially nucleated semiconductor nanowires based on metallic nanoparticle-induced formation of self-assembled nanowires. Further development of the vapor–liquid–solid growth method have made it possible to control not only the dimension and position of nanowires but also to control heterostructures formed inside the nanowires. Based on these techniques we have realized a series of transport devices such as resonant tunneling and single-electron transistors but also optically active single quantum dots positioned inside nanowires displaying sharp emission characteristics due to excitons.     

The elastic properties and energy characteristics of Au nanowires: an atomistic simulation study

This paper have performed molecular static calculations with the quantum corrected Sutten Chen type many body potential to study size effects on the elastic modulus of Au nanowires with [100], [110] and [111] crystallographic directions, and to explore the preferential growth orientation of Au nanowires. The main focus of this work is the size effects on their surface characteristics. Using the common neighbour analysis, this paper deduces that surface region approximately consists of two layer atoms. Further, it extracts the elastic modulus of surface, and calculate surface energy of nanowire. The results show that for all three directions the Young＇s modulus of nanowire increases as the diameter increases. Similar trend has been observed for the Young＇s modulus of surface. However, the atomic average potential energy of nanowire shows an opposite change. Both the potential and surface energy of [110] nanowire are the lowest among all three orlentational nanowires, which helps to explain why Au nanowires possess a [110] preferred orientation during the experimental growth proceeds.     

Silver nanowires for photonics applications

Although silver nanowires as plasmonic components have been investigated extensively in both theoretical and experimental studies, a systematic study is still lacking. In this work, a review is given to explain some basic features of experimentally prepared nanowires and their optical properties in different situations, such as waveguides, resonators, and antennas. The review also lists several possible applications of nanowires for enhanced light‐emitting, photonic device fabrication, sensors, lasers, and nonlinear optics. Combined with the merits of both nanowires and surface plasmon polaritons, silver nanowires are certain to show their potential in photonics in the near future.     

Electrical and photovoltaic characterisations of methyl red dye doped solid-state photoelectrochemical cell

In this work, we have reported the electrical and photovoltaic properties of methyl red dye sensitised photoelectrochemical cell. Here, we have explored the possibility of using methyl red dye in photovoltaic devices. The dye was dispersed in polyvinyl alcohol used as an inert polymer binder and polyethylene oxide complexed with lithium perchlorate ion salt as a solid electrolyte. Ethylene carbonate and propylene carbonate are used as plasticisers. A thin film of this blend is sandwiched between two electrodes, one of which is indium tin oxide coated glass plate and another is aluminium. The active area of the cell is 0.04 cm². By analysing dark I–V characteristics, trap energy is estimated in the order of 0.053 eV. The photovoltaic parameters such as open circuit voltage, short circuit current, fill factor and power conversion efficiency of the cell have been calculated to be 368 mV, 410 nA, 0.349 and 1.24%, respectively. The photovoltaic currents were measured with different intensity.     

The effect of various solvent additives on the power conversion efficiency of polymer-polymer solar cells

We investigated the effect of three different additives (1-chloronaphthalene, 1,8-diiodooctane, diphenylether) on the performance of polymer-polymer solar cells based on a BHJ blend consisting of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) as a donor and poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)) as an acceptor. A direct comparison of the efficiency of the solar cells with and without additive indicated that the device using the additive exhibited slightly improved performance. However, the efficiency enhancement was not significant. The optimal ratio of additive differed depending on the properties of the additive. In addition, the performances of polymer-polymer solar cells were not significantly dependent on the type of additive. Identifying the optimal fabrication condition was critical for achieving the highest performance. It is known that the general role of an additive in polymer solar cells based on a BHJ active layer was to induce good phase separation between the donor and acceptor by morphology modification. However, grazing-incidence wide-angle X-ray scattering results showed that no significant morphology change in polymer-polymer active layer was caused by the additive. Rather, our modulated impedance spectroscopy study showed that the performance enhancement in polymer-polymer solar cells with additive was because of improved recombination properties rather than improvements in crystalline morphology.     

Energy dependence of electron mobility in metallic nanowires

We study the electron drift mobility in a metallic nanowire (at low temperature) as a function of both electron energy and electrochemical potential from considerations relative to energy-dependent conductance and carrier spatial density. In fact, a mathematical expression for the electron mobility, when electronic energy equals Fermi energy (resonant states), valid for negative values of the electrochemical potential is derived.     

梯度掺杂体异质结对有机太阳能电池光电转换效率的影响

基于传统的体异质结有机太阳能电池结构, 对结构中的混合层改用梯度掺杂的方法, 在AM1.5, 100 mW/cm²光照下, 使得器件的短路电流由原来的7.72 mA/cm²提高到了9.18 mA/cm², 相应的光电转换效率提高了25%. 器件性能的提升归因于梯度掺杂体系的引入使得体异质结混合层中同一材料分子之间形成了较好的连续网络结构, 降低了器件的串联电阻, 提高了电极对载流子的收集效率, 从而提高了器件的光电转换效率. 关键词： 有机太阳能电池 体异质结 梯度掺杂