bluuebunny/crossref_metadata_2025 huggingface dataset:
ULTRA-COLD GASES AND THE DETECTION OF THE EARTH'S ROTATION: BOGOLIUBOV SPACE AND GRAVITOMAGNETISM
Authors: CAMACHO A. , CASTELLANOS E.
Published: October 2012

The present work analyses the consequences of the gravitomagnetic effect of the Earth upon a bosonic gas in which the corresponding atoms have a nonvanishing orbital angular momentum. Concerning the ground state of the Bogoliubov space of this system we deduce the consequences, on the pressure and on the speed of sound, of the gravitomagnetic effect. We prove that the effect on a single atom is very small, but we also show that for some thermodynamical properties the consequences scale as a nontrivial function of the number of particles.
A TORSIONAL MODEL OF LEPTONS
Authors: FABBRI LUCA
Published: October 2012

Quite recently it was shown that torsion induces interactions among leptons that are identical to the weak interactions of leptons of the Weinberg Standard Model, if it is in terms of leptonic bound states that the bosonic sector is built; here we obtain the partially conserved axial currents showing that they are the same of the Standard Model, if the composite mediators have specific mass relationships: we show that their masses are indeed the measured ones, if reasonable approximations are taken.
QUANTUM DISCORD, DECOHERENCE AND QUANTUM PHASE TRANSITION
Authors: BOSE INDRANI , PAL AMIT KUMAR
Published: October 2012

Quantum discord is a more general measure of quantum correlations than entanglement and has been proposed as a resource in certain quantum information processing tasks. The computation of discord is mostly confined to two-qubit systems for which an analytical calculational scheme is available. The utilization of quantum correlations in quantum information-based applications is limited by the problem of decoherence, i.e., the loss of coherence due to the inevitable interaction of a quantum system with its environment. The dynamics of quantum correlations due to decoherence may be studied in the Kraus operator formalism for different types of quantum channels representing system-environment interactions. In this review, we describe the salient features of the dynamics of classical and quantum correlations in a two-qubit system under Markovian (memoryless) time evolution. The two-qubit state considered is described by the reduced density matrix obtained from the ground state of a spin model. The models considered include the transverse-field XY model in one dimension, a special case of which is the transverse-field Ising model, and the XXZ spin chain. The quantum channels studied include the amplitude damping, bit-flip, bit-phase-flip and phase-flip channels. The Kraus operator formalism is briefly introduced and the origins of different types of dynamics discussed. One can identify appropriate quantities associated with the dynamics of quantum correlations which provide signatures of quantum phase transitions in the spin models. Experimental observations of the different types of dynamics are also mentioned.
DIRECTLY OBSERVING ENTROPY ACCUMULATION ON THE HORIZON AND HOLOGRAPHY
Authors: EDERY ARIEL , BEAUCHESNE HUGUES
Published: October 2012

Recent numerical simulations of gravitational collapse show that there exists a special foliation of the spacetime where matter and entropy accumulate directly on the inside of the horizon surface. In this foliation, the time coincides with the proper time of the asymptotic static observer (ASO) and for spherical symmetry, this corresponds to isotropic co-ordinates. In this gauge, the three-volume in the interior shrinks to zero and only the horizon area remains at the end of collapse. In a different foliation, matter and entropy accumulate in the volume. The entropy is however independent of the foliation. Black hole holography is therefore a mapping from an arbitrary foliation, where information resides in the volume, to the special ASO frame, where it resides directly on the horizon surface.
PARITY VIOLATION AND ELECTRIC DIPOLE MOMENTS IN ATOMS AND MOLECULES
Authors: DZUBA V. A. , FLAMBAUM V. V.
Published: October 2012

We review the current status of the study of parity and time invariance violation in atoms, nuclei and molecules. We focus on parity nonconservation (PNC) in cesium (CS) and three of the most promising areas of research: (i) PNC in a chain of isotopes, (ii) search for nuclear anapole moments, and (iii) search for permanent electric dipole moments (EDMs) of atoms and molecules, which in turn are caused by either an electron EDM or nuclear T, P-odd moments such as a nuclear EDM or nuclear Schiff moment.
HYPERGRAPH RAMSEY NUMBERS AND ADIABATIC QUANTUM ALGORITHM
Authors: QU RI , ZHAO SU-LI , BAO YAN-RU , CAO XIAO-CHUN
Published: October 2012

Gaitan and Clark [Phys. Rev. Lett.108 (2012) 010501] have recently presented a quantum algorithm for the computation of the Ramsey numbers R(m, n) using adiabatic quantum evolution (AQE). We consider that the two-color Ramsey numbers R(m, n; r) for r-uniform hypergraphs can be computed by using the similar ways in Phys. Rev. Lett.108 (2012) 010501. In this paper, we show how the computation of R(m, n; r) can be mapped to a combinatorial optimization problem whose solution be found using AQE.
BEM SIMULATIONS OF POTENTIAL FLOW WITH VISCOUS EFFECTS AS APPLIED TO AN ACOUSTIC BUBBLE
Authors: GOH BING HUI TERENCE , KLASEBOER EVERT , KHOO BOO CHEONG
Published: October 2012

The problem of a rising bubble under acoustic excitation is numerically investigated by means of two boundary element method (BEM) models in this paper. Our approach via BEM is very economical in the requirement of computational resources and yet reasonably accurate. The models have been implemented for the study of a single rising bubble. We now extend our study to introduce acoustic forcing to a bubble whereby the complexity of the problem increases (e.g. inclusion of shape oscillations). We conduct simulations for small to moderate acoustic pressure, driven close to the bubble's resonant frequency and harmonics for a micron-sized bubble for which viscous effects are reported to be of greater significance. Observations are compared with experimental findings with which we attempt to identify and investigate respectively, the associated conditions and mechanisms behind some effects (e.g. influence on rise velocity) on an acoustic bubble.
NUMERICAL SIMULATION OF HIGH REYNOLDS NUMBER TURBULENT FLOW IN A VANE PASSAGE
Authors: HUANG J. F. , ZHANG L. X. , GUO Y. K.
Published: October 2012

The numerical simulations of two-dimensional high Reynolds number turbulent flow in a guide vane passage of a Francis hydro turbine are performed successfully by using the unstructured dynamic mesh model for moving body. The standard K – ε turbulence model is employed for the simulation of turbulence. The pressure-velocity coupling method is realized with the SIMPLEC algorithm. The temporal distributions of the pressure and turbulent viscosity in a passage were obtained in the closing of wicket gate on a platform of the software ANSYS FLUENT. The results show that the evolution of the flow field is unsteady with decrease of the geometrical opening of the gate. The details of the flow changes are obtained in the moving rigid body domain. The method can be used to simulate the high Reynolds number incompressible turbulent flow with moving boundary. The calculation provides some references for vortex-induced vibration of the structure in a complex turbulent flow.
IMPULSIVELY STARTED FLOW TOPOLOGY AROUND TANDEM ARRANGEMENT OF TWO SQUARE CYLINDER AT INCIDENCE
Authors: DASH SUNIL MANOHAR , LEE THONG-SEE
Published: October 2012

Numerical study of impulsively started flow over two tandem square cylinders where former cylinder is rotated at angles (0-45deg) to main stream flow direction keeping later one inline to flow stream with a separation of twice the side length of square prism between the centers of cylinders is performed using FVM code solver FLUENT 6.3.26. Temporal developments of streamlines around cylinders are studied for laminar flow regime ( Re = 100). Flow pattern formed are categories into Type-1, Type-2, Type-3 & Type-4 as per vortices growth at corresponding angle of incidence which are novel results of present study. Pressure distributions over the surface of cylinders are also monitored.
TRANSIENT DYNAMICS OF STREAK AND LONGITUDINAL VORTICES IN SHEAR FLOW WITH WAVE
Authors: ZHAO MING , GHIDAOUI MOHAMED S.
Published: October 2012

Langmuir circulations are alternating right and left helical vortices in the ocean having horizontal axes parallel to the wind. They are manifested by floating material on the ocean surface as streaks. The laboratory wind driven shear flow demonstrate streak feature with/without wave condition. When the wave is present the explanation of results with Craik-Leibovich instability mechanism, originally proposed for weak current shear in ocean, is not appropriate for some problem as in the laboratory the current shear is strong. The existing normal mode analysis based on the generalized Lagrangian mean formulation for wave with strong shear is not able to capture the fully dynamics of streak and longitudinal vortices. We extend Craik-Leibovich theory to strong shear in Eulerian framework but focusing on the fully perturbation evolution dynamics. Transient dynamics of perturbation is studied with an initial value problem. In this approach the effect of shear and wave and its interaction are made clear. The transient growth in the time period without wave is significant and is crucial to the initial preferred wave number observed in the experiments. The optimal longitudinal vortex form perturbation is searched and the preferred spanwise wave number predicted is well consistent with experimental data of wind shear and wave.
SEPARATING PLASMA AND BLOOD CELLS BY DIELECTROPHORESIS IN MICROFLUIDIC CHIPS
Authors: LEU TZONG-SHYNG , LIAO ZHI-FENG
Published: October 2012

In this paper, a dielectrophoretic (DEP) micro separator is studied for plasma-blood separation. DEP forces created by non-uniform electric fields are used as deflected forces to deplete blood cells from side walls at a given inlet flow rate ( Qin ). Then one can extract plasma through a microchannel on side wall at certain extraction flow rate ( Qp ). In this experiment, saline isotonic solution is chosen as dilute solution for whole blood. The minimum dilute ratio (whole blood: saline dilute) is found to be 1:3 for DEP to substantially deplete blood cells from side walls. Exraction of plasma from whole blood sample by DEP force is also investigated. Experimental results show blood cells do not enter side channel by DEP force at inlet flow rate Qin =0.5 μ1/ min when plasma extract flow rates is Qp ≤ 0.3 μ1/ min . By calculating pure plasma extraction volume fraction, the efficiency in current experiment can reach as high as 20% if dilute ratio 1:3 of whole blood sample is considered.
PARTICLE-FREE EXTRACTION BY USING MICROCHANNEL STRUCTURES
Authors: LEU TZONG-SHYNG , PAI CHING-YI
Published: October 2012

Modern separation methods of particles are usually prepared by large equipments. In this study, microfluidic chips with backward-facing-step (BFS) microchannel structures and centrifugal force are used to extract particle-free fluid from physical samples at the branch. Numerical simulation and experimental studies were performed to investigate the effects of inlet Reynolds number ( Re 0), as well as the particle-free fluid outlet Reynolds number ( Re 1), on the minimum radius of particles (R) that can be excluded from the particle-free fluid outlet channel. The fraction of the volumetric flow rate of particle-free extraction α (=extraction flow rate/inlet flow rate) was also obtained to evaluate the efficiency of particle-free extraction. Based on the numerical and experimental results, it is found that the design with 90° elbow inlet channel has a better performance than straight inlet channel. In this experiment, 1.0 μm radius of particles can be successfully separated from the fluid, and the volumetric fraction of the extraction flow rate was approximately 1.8% when inlet and outlet Reynolds numbers are 90 and 3.0 respectively.
STRUCTURE FORMATION IN SPECTRALLY CONDENSED TURBULENCE
Authors: XIA HUA , SHATS MICHAEL
Published: October 2012

Two-dimensional (2D) turbulence supports the inverse energy cascade and the spectral condensate generation, which are studied in laboratory experiments. The generation of the spectral condensation via the inverse energy cascade dramatically reduces the radial transport in 2D flows. In this paper we report experimental results related to the formation of spectral condensates. The dynamics of the structural formation is reposted.
STUDY OF STRESS AND STRAIN RATES IN A ROTATING CYLINDER SUBJECTED TO INTERNAL AND EXTERNAL PRESSURE
Authors: CHAMOLI NEERAJ , RATTAN MINTO , SINGH SATYA BIR
Published: October 2012

The creep behavior of a thick walled hollow circular cylinder, made of aluminum silicon carbide particulate composite material has been investigated in the present study and creep behavior in this case is assumed to follow Sherby's constitutive model. The stress and strain rate distributions of cylinder rotating about its own axis, have been obtained using von Mises and Tresca yield criteria. The effect of pressure on the stresses and strain rates in the cylinder has been investigated and it is observed that with the increase of the internal pressure in the cylinder the strain rate increases. The introduction of external pressure along with the internal pressure causes the strain rates to decrease. It is also observed that the values of effective stress and strain rate obtained using Tresca criterion are higher than those obtained using Mises criterion. Thus it is suggested to use Tresca criterion for the analysis while designing the cylinder.
Spatially Resolved Electroluminescence Imaging of Shunt Sources in Crystalline Silicon Solar Cells
Authors: Sugimura Emi , Takamoto Sohichiroh , Tsujii Shinichiro , Hirata Kenji , Tani Ayumi , Fuyuki Takashi
Published: October 2012

Electroluminescence (EL) under forward bias represents the total excess minority carrier density in cells. In contrast, EL under reverse bias can be detected as hot spots, which are closely related to harmful current shunt paths. In this study, we detected the shunt position using two kinds of EL. Additionally, we analyzed by the positions and origins of shunt sources using electron-beam-induced-current, lock-in thermography, and an electron-probe-micro analyser. We found two kinds of shunt and we detected a defect located in the depletion layer. We proposed shunt models in the depletion layer using the band model.
Influences of p- and n-Doped Czochralski Base Material on the Performance of Silicon Based Heterojunction Solar Cells
Authors: Ziegler Johannes , Montesdeoca-Santana Amada , Platt Dominik , Hohage Stefan , Guerrero-Lemus Ricardo , Borchert Dietmar
Published: October 2012

In this work we present a cell process for amorphous crystalline silicon heterojunction (SHJ) solar cells based on process steps well known in the photovoltaic industry. All amorphous silicon layers are deposited by plasma enhanced chemical vapor deposition (PECVD) in a one chamber direct plasma reactor working at a radio frequency of 13.56 MHz. The main focus of this work is to study the influence of p- and n-doped Czochralski (Cz) silicon base material with different surface morphology on the cell results of amorphous crystalline SHJ solar cells with intrinsic thin layers. Open circuit voltages V
oc of up to 700 mV are obtained on n-type Cz based SHJ cells (area 100 cm2) with rough surfaces. On p-type Cz based SHJ cells open circuit voltages were limited by the minority carrier bulk lifetime of the used base material.
High Efficiency Silver-Free Heterojunction Silicon Solar Cell
Authors: Hernández José Luis , Yoshikawa Kunta , Feltrin Andrea , Menou Nicolas , Valckx Nick , Assche Elisabeth Van , Schroos Dries , Vandersmissen Kevin , Philipsen Harold , Poortmans Jef , Adachi Daisuke , Yoshimi Masashi , Uto Toshihiko , Uzu Hisashi , Kuchiyama Takashi , Allebé Christophe , Nakanishi Naoaki , Terashita Toru , Fujimoto Takahisa , Koizumi Gensuke , Yamamoto Kenji
Published: October 2012

In this work, we present the results of the replacement of silver screen printing on heterojunction crystalline silicon (c-Si) solar cells with a copper metallization scheme that has the potential to reduce the manufacturing cost while improving their performance. We report for the first time silver-free heterojunction c-Si solar cells on 6-in. wafers. The conversion efficiency reached is a record 22.1% for c-Si technology for this wafer size (V
oc = 729 mV, J
sc = 38.3 mA/cm2, FF= 79.1%). The total power generated is more than 5 W for 1-sun illumination, which is a world record. Heat-damp reliability tests show comparable performance for mini-modules fabricated with copper metalized as for conventional silver screen printed heterojunction c-Si solar cells.
Numerical Analysis of Locally Contacted Rear Surface Passivated Silicon Solar Cells
Authors: Rüdiger Marc , Hermle Martin
Published: October 2012

We present a numerical simulation study on the optimization of locally contacted rear surface passivated p-Si solar cells considering float-zone and Czochralski-grown bulk material, latter by taking different amounts of oxygen concentrations into account and, thus, varying the quality of the bulk material. The conversion efficiency potential is figured out by a broad variation of the nominal base resistivity, thickness and rear contact distance of the solar cell. To focus on the bulk and rear side recombination properties, the front side contact and emitter properties have been idealized to avoid recombination losses in this region. It turns out that high level injection effects playing a major role in the description of high resistivity bulk materials.
Computational Fluid Dynamics Modeling of Mono-Silane Siemens Reactor
Authors: Jung Hosub , Park Jong Hoon , Kang Seung Oh , Jeong Jong Hyun , Jeon Soyoung , Jung Jae Hak , Kim Woo Kyoung
Published: October 2012

The computational fluid dynamics-based FLUENT program was employed to model the heat transfer and chemical reaction in a mono-silane Siemens reactor. The kinetic parameters for the 1-step overall reaction SiH4→Si+ 2H2, such as the pre-exponential factor, temperature coefficient, and activation energy, were carefully optimized to satisfy experimental data obtained from the 4-rod Siemens pilot reactor. Established models were successfully used to evaluate the effects of rod diameter, reaction temperature, and reactant gas flow rate on the deposition rate of silicon.
Crystalline Silicon Cells Fabricated by Different Preclean Processes
Authors: Chen Shih-Wei , Chen Sung-Yu , Chen Chien-Hsun , Cai Bing-Lun , Wu Chien-Hung , Du Chen-Hsun , Lu Wen-Haw
Published: October 2012

In this paper, we show that cell efficiency can be improved by simple preclean steps for silicon substrates. A very low reflectance of less than 1% is observed in the wavelength range from 450 to 700 nm for the silicon substrates precleaned using a NaOH solution followed by a gettering process. Lifetime measurements show that the silicon substrates treated by these preclean processes have a significantly improved minority carrier lifetime owing to a better surface condition than untreated silicon substrates. This result is further supported by the performance of the solar cells. A cell efficiency of 18.609% is achieved in the treated silicon substrates with a gain of 2.14% compared with the untreated silicon substrates.
Excellent Passivation of p+ Silicon Surfaces by Inline Plasma Enhanced Chemical Vapor Deposited SiOx/AlOx Stacks
Authors: Lin Fen , Duttagupta Shubham , Shetty Kishan D. , Boreland Matthew , Aberle Armin G. , Hoex Bram
Published: October 2012

Excellent surface passivation of boron emitters is demonstrated for industrial plasma-enhanced chemical vapor deposited (PECVD) SiO
x
/AlO
x
stacks. Emitter saturation current densities of 39 and 34 fA/cm2, respectively, were achieved at 300 K on 80 Ω/sq boron emitters after activation by (i) a standard industrial firing process and (ii) a forming gas anneal followed by industrial firing. We find that the surface passivation by SiO
x
/AlO
x
stack can be effectively controlled by varying the SiO
x
layer thickness. This stack is directly applicable to certain high-efficiency solar cell structures, by optimising the SiO
x
thickness accordingly.
Advanced Light Trapping of High-Efficiency Thin Film Silicon Solar Cells
Authors: Meguro Tomomi , Feltrin Andrea , Suezaki Takashi , Ichikawa Mitsuru , Kuchiyama Takashi , Adachi Daisuke , Inaki Osamu , Yoshikawa Kunta , Koizumi Gensuke , Uzu Hisashi , Ueda Hiroaki , Uto Toshihiko , Fujimoto Takahisa , Irie Toru , Hayakawa Hironori , Nakanishi Naoaki , Yoshimi Masashi , Yamamoto Kenji
Published: October 2012

Kaneka has been proposing and developing the “advanced super-light trapping (ASLT)” structure for thin film silicon solar cells, which incorporates tailored light confinement structures in tandem thin film silicon solar cells to selectively enhance light trapping in top and bottom subcells. In this paper, we present the results of the development of intermediate reflectors with very low refractive index and the design and implementation of nanoimprinted substrates. We demonstrate that significant current gains are possible by reducing the refractive index of the interlayer beyond state-of-the-art values. In addition, we show that the transparent conductive oxide angular scattering properties correlate with the solar cell performance in the infrared part of the spectrum.
Amorphous-Silicon-Based Thin-Film Solar Cells Exhibiting Low Light-Induced Degradation
Authors: Matsui Takuya , Sai Hitoshi , Saito Kimihiko , Kondo Michio
Published: October 2012

We have applied a triode electrode configuration in the plasma-enhanced chemical vapor deposition (PECVD) process to grow intrinsic hydrogenated amorphous silicon (a-Si:H) light absorbers for the fabrication of p–i–n junction solar cells. Although the deposition rate is lower (0.1–0.3 Å/s) than that of the conventional diode PECVD process, the light-soaking stability of the solar cell is markedly improved and less sensitive to the cell thickness due to the reduced Si–H2 bond density in the a-Si:H i-layer. The a-Si:H single-junction solar cells exhibit low light-induced degradation of conversion efficiency (Δη/ηini∼10%) in comparison with that of high-efficiency solar cells reported to date. By applying the improved a-Si:H layers as top-cell absorbers in a-Si:H/hydrogenated microcrystalline silicon (µc-Si:H) tandem device, the light-induced degradation can be reduced even further (Δη/ηini\lesssim5%). As a result, we obtain confirmed stabilized efficiencies of 9.6 and 11.3% for a-Si:H single-junction and a-Si:H/µc-Si:H tandem solar cells, respectively.
Flattened Light-Scattering Substrate and Its Application to Thin-Film Silicon Solar Cells
Authors: Sai Hitoshi , Kanamori Yoshiaki , Kondo Michio
Published: October 2012

In this study, a flattened light-scattering substrate (FLiSS) with a large refractive index contrast in plane is investigated as an approach for overcoming the detrimental effect of highly textured substrates for obtaining better light management in thin-film silicon solar cells. A FLiSS composed of a two-dimensional ZnO grating and a Ag reflector realize a high open circuit voltage in substrate-type microcrystalline silicon solar cells irrespective of the grating structure, with an enhanced infrared response. The optimum FLiSS structure is discussed with the help of numerical simulation.
Surface Modification of High Haze Front Transparent Conductive Oxide for Silicon Thin Film Solar Cell
Authors: Kim Sun Ho , You Dong Joo , Park Jin Hee , Lee Sung Eun , Lee Heon-Min , Kim Donghwan
Published: October 2012

The aluminium-doped zinc oxide (ZnO:Al) films grown by sputtering method were etched to improve the light scattering property. The high haze value (diffuse transmission to total transmission) of above 40% at 850 nm wavelength was obtained by the increase of etching time. But the resistance of film increased and a lot of pin holes were created due to the over etch for high haze. In order to solve these problems, the additional ZnO layer was deposited on etched ZnO:Al film without sacrifice of high haze. This method was able to compensate the deteriorated properties without the change of optical properties. Amorphous based silicon solar cells showed the improvement of photovoltaic performances by the additional deposition.
CuInSe2-Based Thin-Film Photovoltaic Technology in the Gigawatt Production Era
Authors: Kushiya Katsumi
Published: October 2012

The objective of this paper is to review current status and future prospect on CuInSe2 (CIS)-based thin-film photovoltaic (PV) technology. In CIS-based thin-film PV technology, total-area cell efficiency in a small-area (i.e., smaller than 1 cm2) solar cell with top grids has been over 20%, while aperture-area efficiency in a large-area (i.e., larger than 800 cm2 as definition) monolithic module is approaching to an 18% milestone. However, most of the companies with CIS-based thin-film PV technology still stay at a production research stage, except Solar Frontier K.K. In July, 2011, Solar Frontier has joined the gigawatt (GW) group by starting up their third facility with a 0.9-GW/year production capacity. They are keeping the closest position to pass a 16% module-efficiency border by transferring the developed technologies in the R&D and accelerating the preparation for the future based on the concept of a product life-cycle management.
Fabrication and Characterization of Wide-Gap ZnCuInS2 Solar Cells
Authors: Yamamoto Teruaki , Negami Takayuki , Matsubara Koji , Niki Shigeru
Published: October 2012

We have successfully prepared ZnCuInS2 (Zn2x
Cu1-x
In1-x
S2, ZCIS) thin films by spray pyrolysis deposition (SPD). The bandgap of the ZCIS thin film was widely controlled from 1.4 to 3.4 eV by substituting Zn for Cu and In of CuInS2 (CIS). The resistivity of the ZCIS film was controlled by adjusting deposition temperature and composition ratio. ZCIS solar cells with a structure of glass/indium tin oxide (ITO)/TiO2/In2S3/ZCIS/Au were fabricated. The cell with a bandgap of 1.8 eV showed an efficiency of 4.4%. However, the average V
oc is much lower than what is theoretically possible for absorbers with the bandgap. The secondary ion mass spectroscopy (SIMS) depth profile showed that a narrow bandgap layer, corresponding to a low Zn/(Zn+Cu+In) ratio, was formed at the interface between the buffer and the absorber by interdiffusion. The low V
oc is attributed to the existence of the narrow bandgap layer.
Investigation of Cu(In,Ga)Se2 Solar Cell Performance Deviations in Nominally Equal Absorbers
Authors: Knecht Robin , Parisi Jürgen , Riedel Ingo , Schäffler Raymund , Dimmler Bernhard
Published: October 2012

Cu(In,Ga)Se2 (CIGSe) solar cells were fabricated independently by industrial scale co-evaporation in two separate production lines with the same nominal composition and thickness of the absorber film. Although the device properties were believed to be the same we observed substantial deviations of the respective values of the open circuit voltage (ΔV
OC = 40 mV) and of the fill factor (ΔFF= 4%), whereas the short circuit current was essentially the same. We performed fundamental device analysis, space charge and defect spectroscopy, transient photoluminescence as well as in-depth profiling of the chemical gradients of the absorber films. Using the results from the experiments we set up a simulation baseline which allowed us to conclude that the apparent deviations can be related to the presence of deep recombination centers with different concentration within the CIGSe absorber as well as to variations of the band gap grading.
Transparent Conducting ZnO:B Thin Films Grown by Ultraviolet Light Assisted Metal Organic Chemical Vapor Deposition Using Triethylboron for Cu(In,Ga)Se2 Solar Cells
Authors: Kobayashi Taizo , Yamauchi Kotaro , Mise Takahiro , Nakada Tokio
Published: October 2012

High-efficiency cadmium-free Cu(In,Ga)Se2 (CIGS) thin-film solar cells have been fabricated using a zinc compound buffer layer deposited by the chemical bath deposition (CBD) process. However, the zinc compound buffer layers such as ZnS(O,OH) are prone to plasma-induced damage during the subsequent ZnO sputtering process. A process causing less damage such as metal–organic chemical vapor deposition (MOCVD) is thus required for ZnO-based transparent conducting oxide (TCO) layers. In the present work, the boron-doped zinc oxide (ZnO:B) films were grown by MOCVD using diethyl zinc (DEZ), H2O, and low-toxicity triethylboron (TEB). An UV-assisted MOCVD process was developed in order to reduce the resistivity of ZnO:B films. As a result, the resisitivity significantly decreased together with the increased electron mobility and carrier concentration. The comparison of performance was also carried out for the ZnS(O,OH)/CIGS solar cells with MOCVD-deposited ZnO:B and sputter-deposited ZnO:Al window layers.
Wide-Gap Cu(In,Ga)Se2 Solar Cells with Zn(O,S) Buffer Layers Prepared by Atomic Layer Deposition
Authors: Nakashima Kazuya , Kumazawa Toyokazu , Kobayashi Taizo , Mise Takahiro , Nakada Tokio
Published: October 2012

Wide-gap Cu(In0.4,Ga0.6)Se2 solar cells with Zn(O,S) buffer layers deposited by atomic layer deposition (ALD) technique have been investigated. The band-gap energy (E
g) of the Zn(O,S) layer estimated by optical transmission and reflection measurements was varied from 3.2 to 3.6 eV. The solar cells with sulfur (S)-poor Zn(O,S) buffer layers showed a low open-circuit voltage (V
OC) owing to the cliff nature of the conduction band offset (CBO). In contrast, the solar cells with S-rich Zn(O,S) buffer layers showed a low short-circuit current density (J
SC) owing to the spike nature of CBO. Even if the CBO values were adequate, the best solar cell efficiencies were considerably low. These results suggest that the main cause for the low efficiencies is not interface recombination at the Zn(O,S)/Cu(In,Ga)Se2 interface, but mainly bulk recombination in the Cu(In,Ga)Se2 (CIGS) absorber layer.
Control of Grain in Cu(In,Ga)Se2 Thin Films Prepared by Selenization Method Using Diethylselenide
Authors: Uchikoshi Masaki , Shirakata Sho
Published: October 2012

The relationship between the selenization condition and the grain structure has been studied. A single-phase chalcopyrite Cu(In,Ga)Se2 thin film with densely-packed grains and large grains have been prepared by the two-step selenization of the In/Cu–Ga bilayer precursor using diethylselenide (DESe). The formation of the In–Se compound in the early stage of the first-step selenization (T=350–450 °C) has been found to be important. The succeeding second-step selenization at high temperature of 540 °C led to the well developed (112) grain formation. The relationship between the selenization condition and the CIGS film structure is discussed with relation to the selenization mechanism.
Control of Ga Distribution in Cu(In,Ga)Se2 Photovoltaic Absorber by Solid-State Selenizatoin of CuGa/In/Se/In/CuGa Stack
Authors: Park Jun Seong , Seo Jinu , Park Sang Wook , Jung Woo Jin , Park Nae Man , Kim Jeha , Jeon Chan Wook
Published: October 2012

Among many key parameters required to obtain a record-efficiency Cu(In,Ga)Se2 (CIGS) cell, the band-gap of CIGS should have a double-graded profile in which the band-gap increases toward both of the back and front of the absorber. In an effort to obtain an increased Ga content near the junction area which will raise the band-gap energy of CIGS, a novel metal precursor layered with predetermined amount of Se was annealed in N2 ambient. By inserting the Se layer in between metallic precursor layers, it was found that the front band-gap was increased due to the high Ga content by changing the direction of selenization reaction from inside to outside of metallic precursor. The proposed method is expected to provide a simple process for high quality CIGS photovoltaic absorber layer. The conversion efficiency of 6.80% with J
sc = 37.65 mA/cm2, V
oc = 0.51 V, and FF= 35.4% in an active area of 0.48 cm2 was achieved.
Effects of Antimony Doping on Cu(In1-x,Gax)Se2 Thin Films and Solar Cells
Authors: Yatsushiro Yuta , Nakakoba Hiroya , Mise Takahiro , Kobayashi Taizo , Nakada Tokio
Published: October 2012

The effects of antimony (Sb) doping into Cu(In1-x
,Ga
x
)Se2 (CIGS) thin films and solar cells have been investigated. 10–50-nm-thick Sb thin layers were deposited onto Mo-coated sodalime glass (SLG) and SiO
x
-coated SLG substrates by vacuum evaporation. CIGS thin films were then deposited by a three-stage process at substrate temperatures of 450–550 °C. The grain growth of CIGS thin films was enhanced, and the open-circuit voltage and hence the conversion efficiency improved with the Sb doping when the SLG substrates were used. However, little or no effect was observed when the alkali barrier SiO
x
layer was deposited on SLG substrates. As a result, we found that Sb doping is beneficial for improving the cell performance when sodium exists simultaneously in CIGS layers.
Face-to-Face Annealing Process of Cu2ZnSnS4 Thin Films Deposited by Spray Pyrolysis Method
Authors: Tanaka Kunihiko , Kato Minoru , Goto Koichi , Nakano Yuya , Uchiki Hisao
Published: October 2012

Cu2ZnSnS4 thin films were deposited by the spray pyrolysis method. Copper(II) acetate monohydrate, zinc(II) acetate dihydrate, tin(II) chloride dihydrate, sodium trihydrate, and pure sulfur powder were used as the starting materials of spray pyrolysis solutions, and N,N-dimethylformamide and monoethanolamine were used as the solvent and the stabilizer, respectively. The solution was coated on a Mo-coated soda lime glass substrate and after coating solutions, the films were annealed in a N2 gas atmosphere at 360, 440, and 520 °C with or without placing two films face-to-face. It was found that the face-to-face annealing process prevented losses of S and Sn during the annealing process and the samples annealed with another precursor placed face-to-face at 440 and 520 °C showed narrow and large X-ray diffraction peaks and large grains in the surface images.
Fabrication of Electrodeposited SnS/SnO2 Heterojunction Solar Cells
Authors: Vequizo Junie Jhon M. , Ichimura Masaya
Published: October 2012

SnO2 thin films were successfully electrodeposited from an aqueous oxygen-bubbled tin sulfate solution and partnered with electrodeposited SnS thin films to fabricate SnS/SnO2 heterojunction solar cell. The electrodeposited SnS/SnO2 superstrate structure with 250-°C-annealed SnO2 as a window layer exhibited an open circuit voltage of 40–90 mV and a short circuit current density of 1.5–9.7 mA/cm2. The solar conversion efficiency was estimated to be in the order of 10-2–10-1%. The band discontinuities at the SnS/SnO2 interface were evaluated by X-ray photoelectron spectroscopy. The valence band offset was determined to be approximately 1.85 eV. Using this value and the band gaps of individual layers, the conduction band minimum of SnO2 is predicted to be higher than that of SnS by 0.65 eV.
Wide Band Gap and p-Type Conductive BaCuSeF Thin Films Fabricated by Pulsed Laser Deposition
Authors: Yamazoe Seiji , Yoshikawa Munehiro , Wada Takahiro
Published: October 2012

BaCuSeF films were fabricated on glass substrates for solar cell application. The crystallographic orientation of the films depended on the thickness of the films. The BaCuSeF films with thicknesses of 0.35, 0.6, and 1.0 µm had 102 preferential orientation, and a thicker film of 1.3 µm was polycrystalline. All of the films showed average transmittance of >50% in the visible light region, and the determined band gap energy was 2.8 eV. All of the films showed p-type conductivity of more than 1 S cm-1. The 0.35-µm BaCuSeF film showed the highest p-type conductivity of 19.2 S cm-1. The BaCuSeF is applicable to electrodes for chalcopyrite-based thin film tandem solar cells.
Lattice-Matched Hot Carrier Solar Cell with Energy Selectivity Integrated into Hot Carrier Absorber
Authors: König Dirk , Takeda Yasuhiko , Puthen-Veettil Binesh , Conibeer Gavin
Published: October 2012

We propose a technologically feasible concept of a hot carrier (HC) solar cell (SC) which fulfills the electronic, optical, and to some extent the phononic criteria required. The energy selective process of HCs is implemented into the hot carrier absorber (HCA). Its electronic properties are investigated by a Monte-Carlo code which simulates random deviations of structure thickness and a normal distribution of random elastic electron (e
-) scattering. The structure can be grown epitaxially as a HC-SC test device.
Hot-Carrier Extraction from Intermediate-Band Absorbers through Quantum-Well Energy-Selective Contacts
Authors: Takeda Yasuhiko , Motohiro Tomoyoshi
Published: October 2012

We have revealed that a new scheme of solar cells, i.e., an intermediate-band-assisted hot-carrier solar cell (IB-HC-SC) using energy-selective contacts (ESCs) consisting of quantum wells (QWs) can be a practical solution to achieve significantly high conversion efficiency. There are three requisites unique to hot-carrier extraction for high conversion efficiency: (1) a long thermalization time of carriers in the absorber, (2) a narrow energy-selection width of the ESCs, and (3) a short equilibration time of carriers in the absorber. The use of an intermediate-band (IB) absorber relaxes the first requisite, because the two-step excitation via the IB dramatically suppresses entropy generation associated with hot-carrier extraction that is more remarkable at a shorter thermalization time. The suppression of the entropy generation allows us to use QW-ESCs to solve the issue related to the second requisite involved in practical ESCs consisting of size-distributed quantum dots. The new scheme provides limiting conversion efficiency of around 50% (0.1 sun)–65% (1000 sun) that are significantly higher than those of conventional IB solar cells, when the thermalization time of hot carriers is assumed to be 1 ns.
Impact of a Metal–Organic Vapor Phase Epitaxy Environment on Silicon Substrates for III–V-on-Si Multijunction Solar Cells
Authors: García-Tabarés Elisa , García Iván , Lelièvre Jean-Francois , Rey-Stolle Ignacio
Published: October 2012

With the final goal of integrating III–V materials to silicon for tandem solar cells, the influence of the metal–organic vapor phase epitaxy (MOVPE) environment on the minority carrier properties of silicon wafers has been evaluated. These properties will essentially determine the photovoltaic performance of the bottom cell in a III–V-on-Si tandem solar cell device. A comparison of the base minority carrier lifetimes obtained for different thermal processes carried out in a MOVPE reactor on Czochralski silicon wafers has been carried out. The effect of the formation of the emitter by phosphorus diffusion has also been evaluated.
Characterizing FluidReflex Optical Transfer Function
Authors: Victoria Marta , Domínguez César , Askins Steve , Antón Ignacio , Sala Gabriel
Published: October 2012

FluidReflex is a novel concentrator concept that has been designed to achieve a low cost concentration photovoltaic (CPV) system over 1000× by using reflective optics and a fluid dielectric. In this paper, results regarding the characterization of the concentrator Optical Transfer Function (OTF) are presented. The reflectance and transmittance of the different materials that the concentrator is composed of have been measured using a spectrometer. In addition, a method using component cells (isotypes) has been used to experimentally determine which of the subcells within the multijunction (MJ) solar cell is limiting the current when it is illuminated by the concentrator.
Anomalous Capacitance–Voltage Characteristics of GaAs/AlGaAs Multiple Quantum Well Solar Cells
Authors: Noda Takeshi , Mano Takaaki , Jo Masafumi , Ding Yi , Kawazu Takuya , Sakaki Hiroyuki
Published: October 2012

We study the capacitance–voltage characteristics of GaAs/AlGaAs coupled multiple quantum well (MQW) solar cells. It is found that the capacitance under illumination increases sharply if the bias is raised above -0.2 V, and gets maximum at a bias of about 0.2 V. This increment in capacitance by the illumination is ascribed to the reduction of the depletion layer thickness, caused by the spatially separated accumulation of photogenerated electrons and holes trapped in the MQW layer.
Effects of Background Zn Doping on the Performance of InGaAs/GaAsP Multiple Quantum Well Solar Cells Grown by a Planetary Metal Organic Vapor Phase Epitaxy Reactor
Authors: Sodabanlu Hassanet , Ma Shaojun , Watanabe Kentaroh , Sugiyama Masakazu , Nakano Yoshiaki
Published: October 2012

The effects of background Zn doping on the performance of p–i–n GaAs solar cells with InGaAs/GaAsP multiple quantum wells (MQWs) in i-GaAs layer have been studied. The crystal growth was done by a planetary metalorganic vapor phase epitaxy (MOVPE) reactor. The background Zn doping, in an order of 1017 cm-3, degraded the solar cell efficiency by modifying the energy band diagram in a way that obstructed carrier transports. It was shown by calculation that the carrier transports across the MQWs region suffered from decrease in built-in electric field in absorber layers, leading to an efficiency loss by radiative and nonradiative recombinations. Consequently, the external quantum efficiency and the current density of a Zn-contaminated MQW solar cell were terribly poor. Reactor baking at 850 °C for 20 min seems to remove Zn residues effectively without noticeable effects on the succeeding growth of MQW solar cells. The InGaAs/GaAsP MQWs fabricated in the thermally cleaned reactor have shown a potential to extend the absorption edge of GaAs solar cells and to improve the efficiency of multi-junction solar cells by current matching. Therefore, the growth of InGaAs/GaAsP MQWs by planetary MOVPE reactors requires a careful treatment regarding the background doping issue.
Isotopic Substitution as a Strategy to Control Non-Adiabatic Dynamics in Photoelectrochemical Cells: Surface Complexes between TiO2 and Dicyanomethylene Compounds
Authors: Manzhos Sergei , Fujisawa Jun-ichi , Segawa Hiroshi , Yamashita Koichi
Published: October 2012

We investigate the effect of deuteration on geminate recombination in photoelectrochemical cells operating by interfacial charge transfer absorption bands. The trend in recombination in surface complexes of tetracyanoethylene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and 11,11,12,12-tetracyanonaphtho-2,6-quinodimethane (TCNAQ) with TiO2 is treated as internal conversion (IC) in the model compounds TCNX–O–Ti(OH)3
-. The deuteration of TCNQ and TCNAQ significantly modifies the spectrum of vibronic coupling constants for many vibrational modes, but affects little the modes with the strongest contribution to IC. As a result, the overall effect on recombination/internal conversion is expected to be limited, slightly increasing its rate. We also consider the influence on the recombination of vibrational modes of the Ti(OH)3 moiety which only crudely models the oxide surface. We conclude that even as the model is sensitive to the motions of Ti(OH)3, the predicted trend in recombination in the series TCNE–TCNQ–TCNAQ holds under different treatments of Ti(OH)3 modes.
Nondestructive Three-Dimensional Observation of the Electrolyte in a Dye-Sensitised Solar Cell Combined with the Local Photocurrent Dynamics
Authors: Kawata Kentaro , Yoshizaki Hiroki , Goto Tomohisa , Kato Kazuhiro , Renker Sabine
Published: October 2012

The three-dimensional (3D) visualisation of the photovoltaic active layer in a dye-sensitised solar cell (DSSC) was newly achieved by employing an optical interference measurement system. The technique was used to measure with high precision the active layer thickness of a complete cell to evaluate the diffusion resistance of the electrode layer made of titania and the electrolyte layer containing tetracyanoborate ionic liquid. Additionally, the visualised image was compared with the local photovoltaic characteristics in a region with diameter 100 µm studied using an AC impedance technique as well as by transient photocurrent and photovoltage decay measurements to elucidate the charge transport properties of the ionic-liquid-based electrolyte.
Ag Interlayered Transparent Conducting Electrode for Photovoltaic Cells
Authors: Yang Jeong-Do , Ok Il-Woo , Cho Jung-Min , Park Dong-Hee , Shin Won-Suk , Kim Kyoung-Gon , Moon Sang-Jin , Yoo Kyung-Hwa , Choi Won-Kook
Published: October 2012

We fabricated the organic photovoltaic (OPV) cells on the transparent and low resistive multilayer electrode of a few nm Ag layer embedded Al doped zinc oxide film (AZO/Ag/AZO) on a glass. AZO and Ag consisting of the continuous multilayer were fabricated using rf magnetron at room temperature successively. AZO (45 nm)/Ag (11 nm)/AZO (45 nm) electrode shows an electrical resistivity of 6.56×10-5 Ω cm, optical transmittance of 89.3% at 550 nm and figure of merit (FOM) value of 4.94×10-2 Ω-1. An inverted structure OPV was fabricated on AZO/Ag/AZO transparent electrode in which TiO
x
and PEDOT:PSS were used as an electron transport and hole transport layer respectively. The OPVs showed power conversion efficiency and fill factor as high as 2.07%, 0.51 respectively.
Synthesis and Electrochemical Properties of 2,6-Bis(quinoline-2-yl)pyridyl Ruthenium Complexes as Near-Infrared Sensitizers for Dye-Sensitized Solar Cells
Authors: Onozawa-Komatsuzaki Nobuko , Funaki Takashi , Kasuga Kazuyuki , Nakazawa Yoko , Sayama Kazuhiro , Sugihara Hideki
Published: October 2012

New ruthenium(II)–polypyridyl complexes 1a–1d (1a: X= Y= H, 1b: X= H, Y= Cl, 1c: X= H, Y= Me, 1d: X= COOH, Y= H) having 2,6-bis(4-carboxyquinolin-2-yl)pyridine derivatives as ligands were synthesized as sensitizers for dye-sensitized solar cells (DSCs) and their photophysical and photochemical properties were characterized. The photovoltaic performance of DSCs sensitized with 1a–1d was found to be different. The DSC sensitized with 1a exhibits higher efficiency and IPCE value than those sensitized with 1b–1d. The APCE value of the DSC sensitized with 1a was almost 80% in the 500–800 nm range. Therefore, the performance of the DSC sensitized with 1a might improve if the adsorption of 1a on the TiO2 surface could be appropriately controlled by investigation of dye immersion condition or introduction of bulky substituents on the ligand in order to suppress dye aggregation.
Dye Sensitized Solar Cells Based on Novel Far Red Sensitizing Unsymmetrical Squaraine Dye Containing Pyrroloquinoline Moiety
Authors: Pandey Shyam S. , Fujikawa Naotaka , Watanabe Rie , Ogomi Yuhei , Yamaguchi Yoshihiro , Hayase Shuzi
Published: October 2012

A novel far-red sensitive and direct aromatic ring carboxy functionalized unsymmetrical squaraine dye based on pyrroloquinoline moiety has been synthesized for the application as sensitizer of dye sensitized solar cells. This dye bearing the characteristics of both of indole and quinoline moieties exhibits the photon harvesting up to 820 nm. The enhancement in the photon harvesting window by the pyrroloquinoline based squaraine dye was attributed to the presence of increased π-conjugation in its pyrroloquinoline donor part. This pyrroloquinoline bearing unsymmetrical squaraine dye exhibits a short circuit current density of 9.88 mA/cm2, an open circuit voltage of 0.57 V and fill factor of 0.59 leading to the external power conversion efficiency of 3.33% under simulated solar irradiation of 100 mW/cm2 at AM 1.5 condition.