Volume 80, Issue 10

Since the apparition of the coming energy crises and increased awareness of climate change, various avenues are being explored to replace fossil fuels, with renewable energy from solar power and biomass sources as the most promising. In the last decade, the development of advanced molecular materials and nanotechnologies has initiated a new set of ideas that can dramatically improve energy conversion efficiency and reduce prices of alternative energy sources. It was therefore timely to launch a new initiative as the organization of the interdisciplinary International Conference "Molecular and Nanoscale Systems for Energy Conversion" (MEC-2007), devoted to new research trends in different areas of alternative energetic sources. This event was the first scientific meeting in Russia dealing with the general problems and future challenges in renewable energy conversion. The Conference was held on 1-3 October 2007 in Moscow at the Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, under the sponsorship of the International Union of Pure and Applied Chemistry (IUPAC), the Russian Academy of Sciences, Lomonosov Moscow State University, and the Russian Foundation for Basic Research. The Conference featured 11 oral sessions and a general poster session, which was held throughout the entire duration of the event. Over 200 researchers from 11 countries, including 90 students, participated in the event. The presentations of the latest discoveries included 85 contributed papers and 12 plenary and 9 keynote lectures covering 4 topics: (i) advanced systems for photovoltaics, (ii) new types of fuel cells, (iii) biofuels, and (iv) molecular and nanoscale systems for energy conversion. All submitted abstracts were reviewed by the International Program Committee. In this issue of Pure and Applied Chemistry we introduce a selection of papers based on plenary and keynote lectures delivered at MEC-2007. This volume contains: a discussion of light intensity, asone of the most important factors influencing solar energy conversion (S. D. Varfolomeev, Russia); aviewpoint on future directions in photovoltaics as a new challenge for chemical physics (O. Shevaleevskiy, Russia); a description of new Cu(In,Ga)Se 2 (CIGS) solar cells (B. T. Ahn, South Korea); a description of metal cluster-like materials for the molecular oxygen reduction reaction (N. Alonso-Vante, France); an application of biogas and microbial fuel cell technologies for anaerobicdigestion of wastes (S. V. Kalyuzhnyi, Russia); a description of light energy conversion mechanism indual fluorophoreñnitroxide molecules (G. I. Likhtenshtein, Israel); an overview of dangling-bond (DB)defect behavior in nanocrystalline silicon-based films for photovoltaics (K. S. Lim, South Korea); andan approach to the design of low-bandgap polymer solar cells (D. Yu. Paraschuk, Russia). All of thecontributions exemplify the participants' broad range of interests and characterize the new challengesin the area of renewable energy sources. Sergey Varfolomeev and Oleg Shevaleevskiy Conference Editors

The kinetic model has been developed for disserting the efficiency of solar energy conversion as a function of light intensity. A comparison of theory with experimental results shows that the model provides a satisfactory agreement. We have estimated the essential parameters of photosynthetic systems (the size of the photosynthetic antenna, the rate of electron transport, the correlation between photosynthesis and respiration) that are responsible for reaching the maximum efficiency at "one sun" and "one hundred suns" light illumination intensities. Recommendations for the improvement of photosynthetic system parameters using genetic engineering methods are also provided.

In recent times, photovoltaic (PV) technologies for solar energy conversion have gained greater recognition. World production of PV cells and modules over the last five years grew at an average of around 40 % a year. The history of modern PV science started more than half a century ago. However, the period that followed exploited the mid-20 th century developments in the basics of solid-state physics and semiconductor science. With only a few exceptions, almost no major achievements were attained during a long period of time. The present paper offers an attempt of a critical retrospective look at the history and current progress of solar PV research from a personal viewpoint. It also addresses the current status of research on conventional solid-state PV devices and compares it with the alternative organic and molecular PV systems. The paper briefly describes the potential of new types of organic and mesoscopic dye-sensitized solar cells (DSCs). The paper shows that chemical physics rather than traditional solid-state physics is expected to lead to exciting challenges in the future of PV science.

Recent progress in the field of Cu(In,Ga)Se 2 (CIGS) thin film solar cell technology is briefly reviewed. New wide-bandgap In x (OOH,S) y and ZnS x (OH) y O z buffers for CIGS solar cells have been developed. Advances have been made in the film deposition by the growth process optimization that allows the control of film properties at the micro- and nanolevels. To improve the CIGS cell junction characteristics, we have provided the integration of the developed Cd-free films with a very thin CdS film. Transmittances of the developed buffers were greatly increased compared to the standard CdS. In x (OOH,S) y buffer has been applied to low-bandgap CIGS devices which have shown poor photovoltaic properties. The experimental results obtained suggest that low efficiency can be explained by unfavorable conduction band alignment at the In x (OOH,S) y /CIGS heterojunction. The application of a wide-gap Cu(In,Ga)(Se,S) 2 absorber for device fabrication yields the conversion efficiency of 12.55 %. As a result, the In x (OOH,S) y buffer is promising for wide-bandgap Cu(In,Ga)(Se,S) 2 solar cells, however, its exploration for low-bandgap CIGS devices will not allow a high conversion efficiency. The role played by interdiffusion at the double-buffer/CIGS heterojunction and its impact on the electronic structure and device performance has also been discussed.

Research of nanometer scale range catalysts based on cluster-like mono-, bi-metallic, and chalcogenides for oxygen reduction reaction (ORR) as cathodes, a major challenge for polymer electrolyte membrane fuel cells (PEMFCs) nowadays, for facilitating efficient electron transfer using the carbonyl chemical route is reviewed. A strategy aimed at reducing the amount of expensive catalyst materials, giving the accessibility of non-noble materials and taking into account the activity and selectivity of cathodes for the ORR is devised as well.

The well-known use of the microbiological process of anaerobic digestion (AD) to generate biogas (mixture of methane and CO 2 ) is now widely implemented for the production of renewable energy worldwide. In Russia, however, this is not the case despite huge amounts of organic wastes (OW) suitable for AD. This paper firstly inventories major flows of OW from various sectors of the national economy (agriculture, industry, households, etc.) and estimates their biogas potential. Special attention is paid to existing bottlenecks and barriers to implementation of biogas technology given the Russian socioeconomic conditions. The second part of the paper is devoted to a new emerging technology based on AD-microbial fuel cells (MFCs). The current status of research in this field in Russia is reviewed in comparison with worldwide developments. The possible niches for implementation of MFC technology in Russia (e.g., wastewater treatment) are pointed out, including its complements to conventional biogas processes.

Donor-acceptor structures capable of retaining the charge-photoseparated state during the time long enough for secondary chemical reactions of these charges to occur attract special interest from the viewpoint of the problem of light energy utilization. We proposed dual fluorophore-nitroxide compounds ( FNO • ) as systems for the conversion of light energy to chemical energy. In these systems, the fluorophore segment in the excited singlet state serves as an electron donor, and the nitroxide segment is an electron acceptor. In FNO • , the photo- and chemical reduction of nitroxide results in the drastic decay of the electron spin resonance (ESR) signal from the nitroxide and the parallel enhancement of fluorescence. The same groups allow one to measure the factors affecting the electron transfer, namely, molecular dynamics and micropolarity of the medium in the vicinity of the donor (by fluorescence technique) and acceptor (by ESR) moieties. We demonstrate that in the dual probes the nitroxide segment is photoreduced to hydroxylamine in solution and in such nanoscale structures as serum albumins. The photoreduction occurs by very weak reducing agents (glycerol, ethanol, ethylene glycol, etc.) without a violation of the fluorophore structure. Therefore, photochemical reactions in the dual compounds with the formation of a reducing agent as hydroxyl amine can be considered as processes of light energy transfer. The nitroxide segment tethered to the donor-bridge-acceptor triad affects the photoseparated charge recombination via the mechanism of spin catalysis. Proficiency of the dual compounds for developing energy conversion systems can be extended by an optimal choice of the participants of the photochemical and -physical processes.

Thin films of microcrystalline hydrogenated silicon (µc-Si:H) and nanocrystalline silicon carbide (nc-SiC:H) provide a new class of advanced nanostructured materials for solar photovoltaic (PV) devices. We have worked on the fabrication, characterization, and application of these materials for thin film PV solar cells based on amorphous silicon. Here we present an overview of the preparation and characterization methods for heterogeneous SiC:H-based layers. Hydrogenated nc-SiC:H thin film materials with high crystalline volume fraction were deposited using photo-assisted chemical vapor deposition (photo-CVD) technique. The behavior of spin-containing dangling-bond (DB) defects was performed using electron spin resonance (ESR) and transport measurements as a function of sample crystallinity, doping level, and temperature. The electronic and structural properties of intrinsic and doped µc-Si:H and nc-SiC:H thin films are reviewed with the emphasis of the essential role of DB defects on the photoelectronic transport parameters.

Polymer solar cells have shown high potential to convert solar energy into electricity in a cost-effective way. One of the basic reasons limiting the polymer solar cell efficiency is insufficient absorption of the solar radiation by the active layer that limits the photocurrent. To increase the photocurrent, one needs low-bandgap materials with strong absorption below 2 eV. In this work, we study two types of low-bandgap materials: ground-state charge-transfer complexes (CTCs) of a conjugated polymer, MEH-PPV (poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene]), and an exohedral metallocomplex of fullerene, (η 2 -C 60 )IrH(CO)[(+)DIOP] (IrC 60 ). We demonstrate that the CTC formed between MEH-PPV and conjugated molecules with high electron affinity, namely, 2,4,7-trinitrofluorenone (TNF) and 1,5-dinitroantraquinone (DNAQ), can have strong optical absorption extending down to the near infrared. We have observed that the photoexcited CTC can generate free charges. We also report on optical studies of IrC 60 as a possible acceptor for polymer/fullerene solar cells. IrC 60 strongly absorbs in the visible spectral range, in particular in the red part, and therefore has a potential for increasing the photocurrent as compared with polymer/methanofullerene solar cells. Our studies of MEH-PPV/IrC 60 blended films show that long-lived charges are efficiently generated at MEH-PPV upon photoexcitation of the blend.

This document presents recommended definitions of basic terms related to polymerization processes. Recent developments relating to the kinetics, thermodynamics, and mechanisms of polymerization have necessitated the introduction of new terms and some revision or augmentation of terms previously defined in the Compendium of Chemical Terminology (the "Gold Book") or the IUPAC "Glossary of Basic Terms in Polymer Science".

This Technical Report compiles and analyzes the current scientific knowledge on herbal medicine and highlights the practical ways for ensuring the safety of herbal preparations and evaluating their claimed efficacy. Emphasis has been given to the methods for standardization of herbal medicine and the ways and means for moving forward to achieve the difficult goal of preparing herbal medicines of consistent quality and effects. Pragmatic approaches have been recommended to overcome the difficulties in (i) protecting intellectual property rights (IPR); (ii) producing safe, potent, standardized, and affordable herbal medicine; and (iii) documenting the knowledge base on herbal medicine in an easily accessible format.