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Circuit Conditions (circuit + condition)

Distribution by Scientific Domains
Physics and Astronomy40%

Selected Abstracts

Photoluminescence and time-resolved photoluminescence in Cu(In,Ga)Se2 thin films and solar cells

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009
Sho Shirakata
Abstract Photoluminescence (PL) and time-resolved PL (TR-PL) studies have been carried out on Cu(In,Ga)Se2 (CIGS) thin films and solar cells (ZnO/CdS/CIGS) to study the recombination of the photo-excited carriers. The CIGS solar cells exhibited intense near-band-edge (NBE) PL compared with the CIGS films by two orders of magnitude. PL decay time of the cell is strongly dependent on the repetition frequency of the excitation light. PL decay time of the cell is longer than that of the corresponding CIGS thin film. The chemical bath deposition of the CdS buffer layer on CIGS leads to changes in PL intensity, defect-related PL and the PL decay time. They are discussed with relation to the substitution of Cd atom at the Cu site at the Cu-deficient surface of CIGS thin film. Under the open circuit condition, NBE-PL is stronger and the decay time is longer compared with those under the short circuit condition. PL of the cell under the load was examined, and PL intensity and PL decay time are related to the photovoltage during PL measurements. Low temperature PL suggests that the Cd diffusion during the CBD process is pronounced for low Ga content CIGS. The authors demonstrate the effectiveness of PL as a powerful non-destructive device and photovoltaic characterization methods of CIGS solar cells. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Energy effect in switching of PAR thin film as an electrical bistable material

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2004
Hengbo Xie
Abstract A PAR thin film involved in a sandwich structure of Al/PAR/Al was prepared by vacuum evaporation. The electrical bistable switching phenomenon of the PAR thin film was studied under different circuit conditions. An intermediate state with nonlinear resistance was observed when the impedance of the film changed from high to low. Furthermore, an energy effect was found during the transition, i.e. when the applied voltage exceeded a certain value the energy consumption during the whole transition remained invariable. The results indicate that it is not the applied voltage or the current, but the energy that controls the switching process. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

High potential of thin (<1,µm) a-Si: H/µc-Si:H tandem solar cells

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 2 2010
S. Schicho
Abstract Silicon based thin tandem solar cells were fabricated by plasma enhanced chemical vapor deposition (PECVD) in a 30,×,30,cm2 reactor. The layer thicknesses of the amorphous top cells and the microcrystalline bottom cells were significantly reduced compared to standard tandem cells that are optimized for high efficiency (typically with a total absorber layer thickness from 1.5 to 3,µm). The individual absorber layer thicknesses of the top and bottom cells were chosen so that the generated current densities are similar to each other. With such thin cells, having a total absorber layer thickness varying from 0.5 to 1.5,µm, initial efficiencies of 8.6,10.7% were achieved. The effects of thickness variations of both absorber layers on the device properties have been separately investigated. With the help of quantum efficiency (QE) measurements, we could demonstrate that by reducing the bottom cell thickness the top cell current density increased which is addressed to back-reflected light. Due to a very thin a-Si:H top cell, the thin tandem cells show a much lower degradation rate under continuous illumination at open circuit conditions compared to standard tandem and a-Si:H single junction cells. We demonstrate that thin tandem cells of around 550,nm show better stabilized efficiencies than a-Si:H and µc-Si:H single junction cells of comparable thickness. The results show the high potential of thin a-Si/µc-Si tandem cells for cost-effective photovoltaics. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Impedance spectroscopy as a tool for non-intrusive detection of extracellular mediators in microbial fuel cells

BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009
Ramaraja P. Ramasamy
Abstract Endogenously produced, diffusible redox mediators can act as electron shuttles for bacterial respiration. Accordingly, the mediators also serve a critical role in microbial fuel cells (MFCs), as they assist extracellular electron transfer from the bacteria to the anode serving as the intermediate electron sink. Electrochemical impedance spectroscopy (EIS) may be a valuable tool for evaluating the role of mediators in an operating MFC. EIS offers distinct advantages over some conventional analytical methods for the investigation of MFC systems because EIS can elucidate the electrochemical properties of various charge transfer processes in the bio-energetic pathway. Preliminary investigations of Shewanella oneidensis DSP10-based MFCs revealved that even low quantities of extracellular mediators significantly influence the impedance behavior of MFCs. EIS results also suggested that for the model MFC studied, electron transfer from the mediator to the anode may be up to 15 times faster than the electron transfer from bacteria to the mediator. When a simple carbonate membrane separated the anode and cathode chambers, the extracellular mediators were also detected at the cathode, indicating diffusion from the anode under open circuit conditions. The findings demonstrated that EIS can be used as a tool to indicate presence of extracellular redox mediators produced by microorganisms and their participation in extracellular electron shuttling. Biotechnol. Bioeng. 2009; 104: 882,891. © 2009 Wiley Periodicals, Inc. [source]

The Influence of Charge Transport and Recombination on the Performance of Dye-Sensitized Solar Cells

CHEMPHYSCHEM, Issue 1 2009
Mingkui Wang Dr.
Abstract Electrochemical impedance spectroscopy (EIS) and transient voltage decay measurements are applied to compare the performance of dye sensitized solar cells (DSCs) using organic electrolytes, ionic liquids and organic-hole conductors as hole transport materials (HTM). Nano-crystalline titania films sensitized by the same heteroleptic ruthenium complex NaRu(4-carboxylic acid-4,-carboxylate) (4,4,-dinonyl-2,2,-bipyridyl)(NCS)2,, coded Z-907Na are employed as working electrodes. The influence of the nature of the HTM on the photovoltaic figures of merit, that is, the open circuit voltage, short circuit photocurrent and fill factor is evaluated. In order to derive the electron lifetime, as well as the electron diffusion coefficient and charge collection efficiency, EIS measurements are performed in the dark and under illumination corresponding to realistic photovoltaic operating conditions of these mesoscopic solar cells. A theoretical model is established to interpret the frequency response off the impedance under open circuit conditions, which is conceptually similar to photovoltage transient decay measurements. Important information on factors that govern the dynamics of electron transport within the nanocrystalline TiO2 film and charge recombination across the dye sensitized heterojunction is obtained. [source]