bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Zn and Mg doping on CuInS thin films and solar cells
Authors: Enzenhofer Tobias , Unold Thomas , Scheer Roland , Schock Hans-Werner 
Published: November 2011

AbstractSolar cells based on CuInS2 still suffer from Voc limitation compared to the value expected from the bandgap. The open circuit voltage can be enhanced via controlled doping of small amounts of Zinc or Magnesium (< 1 at. %), however the underlying physical reason for this improvement is not understood so far. We have systematically studied the effect of diffusion of Zn and Mg into the absorber layers with photoluminescence and quantum efficiency measurements. ZnO (ZnMgO, MgF2) has been deposited onto the absorber layers and photoluminescence (PL) spectra at room temperature were recorded as a function of the annealing temperature. The modified emission spectra reveal a defect related transition with a strong luminescence signal. At the same time the open-circuit voltage of the Zn (Mg) doped CuInS2 cells are around 100 mV higher than the values found for the undoped cells from the same device process. We interpret these results as a reduced defect state density at the surface and an increased bulk defect concentration induced by the incorporation of Zn or Mg. Comparison of external quantum efficiency (EQE) and I/U measurements with the PL results support observed changes of the interface/bulk properties.
High-Efficiency CdTe Polycrystalline Thin-Film Solar Cells with an Ultra-Thin CuxTe Transparent Back-Contact
Authors: Wu X. , Zhou J. , Duda A. , Keane J. C. , Gessert T.A. , Yan Y. , Noufi R. 
Published: November 2011

AbstractTo fabricate a high-efficiency polycrystalline thin-film tandem cell, the most critical work is to make a high-efficiency top cell (>15%) with high bandgap (Eg=1.5-1.8 eV) and high transmission (T>70%) in the near-infrared (NIR) wavelength region. The CdTe cell is one of the candidates for the top cell, because CdTe state-of-the-art single-junction devices with efficiencies of more than 16% are available, although its bandgap (1.48 eV) is slightly lower for a top cell in a dual-junction device. In this paper, we focus on the development of an ultra-thin, low-bandgap CuxTe transparent back-contact to produce high-efficiency CdTe cells with high NIR transmission. We have achieved an NREL-confirmed 13.9%-efficient CdTe transparent solar cell with an infrared transmission of ~50% and a CdTe/CIS polycrystalline mechanically stacked thin-film tandem cell with an NREL-confirmed efficiency of 15.3%.
Simulation of Polycrystalline Cu(In,Ga)Se2 Solar Cells in Two Dimensions
Authors: Gloeckler Markus , Metzger Wyatt K. , Sites James R. 
Published: November 2011

AbstractThe extent to which grain boundaries (GBs) in polycrystalline materials may be detrimental, benign, or even beneficial is explored with numerical simulations in two dimensions. We focus on the effects of GB recombination in Cu(In,Ga)Se2 (CIGS) solar cells and its effects on solar-cell performance. The simulations predict that (1) for device effciency exceeding 17%, the effective GB recombination velocity must be less than 104 cm/s; (2) grain boundaries within the space-charge region (SCR) lower the open-circuit voltage, whereas the short-circuit current is reduced by grain boundaries in the bulk material; and (3) horizontal GBs are relatively benign unless they are located in the SCR. Modifications to the electronic structure near grain boundaries show that charge-induced band-bending at grain boundaries will most likely have a negative effect on device performance, whereas a down-shift in the valence-band energy at the grain surface can effectively passivate the GBs and reduce the effective recombination velocity. For the models considered, GBs generally have a deleterious effect on effciency, and GBs alone can not explain the apparent superiority of polycrystalline over single-crystalline CIGS materials.
Effect of Stresses in Molybdenum Back Contact Film on Properties of CIGSS Absorber Layer
Authors: Kadam Ankur A. , Jahagirdar Anant H. , Dhere Neelkanth G. 
Published: November 2011

AbstractAnalysis of CuIn1-x Gax Se2-y Sy (CIGSS) absorber and molybdenum back contact layer was carried out to understand the changes in the microstructure of CIGSS layer as a function of the deposition conditions and the nature of stress in the underlying Mo film. All the depositions were carried out on 10 cm x 10 cm glass substrates. Compressive and tensile stressed molybdenum films were prepared with combinations of deposition parameters; power and pressure. CIGSS absorber layer was prepared by depositing metallic precursors using DC magnetron sputtering followed by selenization and sulfurization. Molybdenum layer deposited at 300 W and 3 x 10 Torr pressure produced compressive stress with compact, well adherent and lower sheet resistance as compared to the tensile stressed film deposited at 200 W and 5 x 10 Torr. The crystallinity of the CIGSS film was found not to depend on the stress in the underlying molybdenum film. However, the adhesion at the Mo/CIGSS as well as gallium profile at the Mo/CIGSS interface were affected by the stress.
Growth Mechanisms of Electrodeposited CuInSe2 and Cu(In,Ga)Se2 Determined by Cyclic Voltammetry
Authors: Calixto M. Estela , Dobson Kevin D. , McCandless Brian E. , Birkmire Robert W. 
Published: November 2011

AbstractElectrodeposition (ED) of CuInSe2-based thin films from a buffered single-bath on dcsputtered Mo layers has been investigated. In order to understand the film growth, cyclic voltammetry (CV) was used to identify mechanisms leading to the formation of CuInSe2 and Cu(In,Ga)Se2. Similar CV data were observed for deposition from Cu-Se, Cu-In-Se, Cu-Ga-Se, and Cu-In-Ga-Se baths. A preliminary mechanism for CuInSe2 and Cu(In,Ga)Se2 film growth has been proposed from CV, composition and glancing incidence x-ray diffraction (GIXRD) data. Incorporation of In into the growing films occurs via reaction with H2Se, formed by reduction of the initially deposited Cu3Se2, to form In2Se3, which is in turn rapidly assimilated into the film by reaction with copper selenides to form CuInSe2. The incorporation of Ga may occur via a similar mechanism, however, the precipitation of Ga(OH)3 can not be ruled out as a possible route for Ga uptake. All as-deposited ED CuInSe2–based films have poor crystallinity and require annealing in H2Se prior to device processing. Preliminary device results are presented, reporting a conversion efficiency of 6.5% and 6.2% for electrodeposited CuInSe2 and Cu(In,Ga)Se2, respectively.
High-Efficient ZnO/PVD-CdS/Cu(In,Ga)Se2 Thin Film Solar Cells: Formation of the Buffer-Absorber Interface and Transport Properties
Authors: Rusu Marin , Glatzel Thilo , Kaufmann Christian A. , Neisser Axel , Siebentritt Susanne , Sadewasser Sascha , Schedel-Niedrig Thomas , Lux-Steiner Martha Ch. 
Published: November 2011

AbstractFor preparation of ZnO/CdS/Cu(In,Ga)Se2 solar cells, physical vapor deposition (PVD) was employed to deposit CdS buffer layers in ultrahigh vacuum on Se-decapped absorber surfaces, thus realizing an all ‘dry' fabrication process of the device. An 14.1% total area and 14.5% active area efficient ZnO/CdS/Cu(In,Ga)Se2 solar cell under AM1.5 conditions was achieved after annealing the as-prepared solar cells in air. Kelvin probe force microscopy (KPFM) measurements were carried out in-situ to monitor the initial growth of the CdS buffer layer on the absorber, as well as its electronic properties, in particular, the work function. It was observed that the PVD-CdS growth is initially inhibited at the absorber grain boundaries. Quantum efficiency measurements allowed us to suppose that during the initial growth stage a passivation of the grain boundaries occurs. The latter explains the higher short-circuit currents of the cells with PVD-CdS compared to their references with CdS grown by chemical bath deposition (CBD). The beneficial effect of the annealing seems to originate from a formation of a region with higher band gap than that of the absorber bulk and inverted conductivity type at the absorber surface, close to the CdS/Cu(In,Ga)Se2 interface, leading to a dramatic change in the electronic transport properties and finally, to a significant enhancement of the open-circuit voltage. Annealing of the ZnO/PVD-CdS/Cu(In,Ga)Se2 solar cells provides formation of PVDCdS/ Cu(In,Ga)Se2 interface with properties similar to that of reference samples with CBD-CdS.
Wide-gap CIGS solar cells with Zn1-yMgyO transparent conducting film
Authors: Matsubara K. , Yamada A. , Ishizuka S. , Sakurai K. , Tampo H. , Kimura Y. , Nakamura S. , Yonemura M. , Nakanishi H. , Niki S. 
Published: November 2011

AbstractZn1-yMgyO bandgap controllable transparent conducting films were used for the wide-gap Cu(In1-xGax)Se2 thin film solar cells. Undoped Zn1-yMgyO and Al doped Zn1-yMgyO films were deposited by co-sputtering using a carousel type sputtering apparatus. Zn1-yMgyO films with Mg content y of up to 0.10 were examined. For Cu(In1-xGax)Se2 with band gap energy ˜1.38 eV, the cell performance was slightly improved by using Zn1-yMgyO and Al doped Zn1-yMgyO instead of ZnO and Al doped ZnO. An unexpected improvement of short circuit current density was observed.
In Situ Sensors for CIGS Deposition and Manufacture
Authors: Repins I.L , Gomez N. , Simpson L. , Joshi B. 
Published: November 2011

AbstractIn situ sensors are an important tool for process control, optimization, and documentation, both in the laboratory and industrial environments. Their further application to deposition of CuInxGa1-xSe2 (CIGS) for photovoltaics is particularly important, as record device efficiencies produced in the laboratory have yet to be replicated in manufacturing. This paper provides an overview of the current state of the art of in situ diagnostics for devices based on coevaporated CIGS.
Cu K-edge EXAFS Studies Of CdCl2 Effects On CdTe Solar Cells
Authors: Liu Xiangxin , Compaan Alvin D. , Terry Jeff 
Published: November 2011

AbstractThe highest performance CdS/CdTe thin film solar cells are generally completed with a Cucontaining back contact. The copper appears to be critical for achieving heavy p-type doping of the CdTe at the contact to permit the formation of a low resistance contact. In previous extended x-ray absorption fine structure (EXAFS) work we have inferred that most of the Cu in CdTe films resides as Cu2O at the boundaries of CdTe grains in films that have received a chloride treatment in the presence of oxygen, a critical step needed to improve the performance of all CdTe thin-film cells. This has suggested a mechanism for grain boundary passivation in thinfilm CdTe solar cells. We believe most of the diffused Cu decorates grain boundaries as oxides, consistent with the low doping densities typically observed in CdTe solar cells. The significance for grain boundary passivation will be discussed. We also find evidence that the grain-boundary Cu2O in CdCl2 treated CdTe films is unstable and tends to transform to CuO under some stress conditions.
Effects of Ge-Implantation on the Photoluminescence of CuGaSe2 Thin Films
Authors: Doka Serge , Rusu Marin , Meeder Alex , Arushanov Ernest , Fabre Norbert , Fiechter Sebastian , Schedel-Niedrig Thomas , Lux-Steiner Martha Ch. 
Published: November 2011

AbstractPhotoluminescence (PL) spectra of as grown Ga-rich, and Ga-rich plus Ge-doped and annealed CCSVT (Chemical Close-Spaced Vapor Transport) — CuGaSe2 thin films have been investigated. Visible (514.5 nm) and Ultra- Violet (351.1 nm) excitation energies of the laser have been used in order to determine intrinsic and extrinsic defects created due to the implantation as well as separating near surface from bulk recombination.Both visible and UV-PL spectra of the undoped films show the well known luminescence of Ga-rich CuGaSe2, which can be described by the widely accepted model of fluctuating potentials. Unlike the visible- and UV-PL emissions of Ge- implanted and annealed films differ strongly. Obviously, Ge-implantation in combination with the thermal treatment results in an extrinsic doping of the material producing so far unknown states in the CuGaSe2 band gap. Comparing the visible- and the UV-PL spectra we found an accumulation of these extrinsic doping levels in the near-surface-region of the films.
Conduction-Band-Offset Rule Governing J-V Distortion in CdS/CI(G)S Solar Cells
Authors: Kanevce A. , Gloeckler M. , Pudov A.O. , Sites J.R. 
Published: November 2011

AbstractA type-I (“spike”) conduction-band offset (CBO) greater than a few tenths of an eV at the n/p interface of a solar cell can lead to significant distortion of the current-voltage (J-V) curve. Such distortion has been observed in CdS/CIS cells, low-gallium CdS/CIGS cells, and CIGS cells with alternative windows that increase the CBO. The basic feature is reduced current collection in forward bias. The distortion is mitigated by photoconductivity in the CdS or other window layer, and it is therefore more severe if the illumination contains no photons with energies greater than the band gap of the window layer. The device-physics analysis of such distortion is numerical simulation incorporating a three-layer [TCO/CdS/CI(G)S] approximation for the solar cell. The parameters that influence the barrier height, and hence the distortion, are the magnitude of the CBO, the doping of the p- and n- layers, the defect density of the CdS, and the thicknesses of the CdS and TCO layers. The key value, however, is the energy difference between the quasi-Fermi level for electrons and the conduction band at the CdS/CIS interface. Thermionic emission across the interface will limit the current collection, if the difference exceeds approximately 0.48 eV at 300 K and one-sun illumination. This constraint is consistent with experiment, and strategies to satisfy the 0.48-eV rule when designing solar cells are enumerated.
Investigating Minority-Carrier Traps in p-type Cu(InGa)Se2 Using Deep Level Transient Spectroscopy
Authors: Johnston Steven W. , AbuShama Jehad A. M. , Noufi Rommel 
Published: November 2011

AbstractMeasurements of p-type Cu(InGa)Se2 (CIGS) using deep-level transient spectroscopy (DLTS) show peaks associated with minority-carrier traps, even though data were collected using reverse bias conditions not favorable to injecting minority-carrier electrons. These DLTS peaks occur in the temperature range of 50 to 150 K for the rate windows used and correspond to electron traps having activation energies usually in the range of 0.1 to 0.2 eV for alloys of CIS, CGS, and CIGS. The peak values also depend on the number of traps filled. For short filling times of 10 μs to 100 μs, a small peak appears. As the DLTS filling pulse width increases, the peak increases in response to more traps being filled, but it also broadens and shifts to lower temperature suggesting that a possible series of trap levels, perhaps forming a defect band, are present. The peaks usually saturate in a timeframe of seconds. These filling times are sufficient for electrons to fill traps near the interface from the n-type side of the device due to a thermionic emission current. Admittance spectroscopy data for the same samples are shown for comparison.
Defects and interfaces in Cu(In,Ga)Se2–based thin-film solar cells with and without Na diffusion barrier
Authors: Heinrich Helge , Senapati Sephalika , Kulkarni Shripad R. , Halbe Ankush R. , Rudmann Dominik , Tiwari Ayodhya N. 
Published: November 2011

AbstractTo characterize the influence of sodium diffusion on the Cu(In,Ga)Se2 (CIGS) layer, samples with and without an A12O3 diffusion barrier were investigated by transmission electron microscopy. The soda lime glass acts as a sodium source for samples without diffusion barrier while a post deposition treatment with NaF adds sodium to the CIGS layer for samples with diffusion barrier. For low deposition temperatures in the three-stage growth process for CIGS slightly columnar CIGS grains near the Mo back contact are found and larger grains near the top surface. Samples subject to high-temperature post deposition treatments show slightly larger grain sizes in the CIGS layer than samples prepared at the same temperature but with sodium from the soda lime glass. The surface smoothness of the CIGS layer and therefore the continuity of the following layers is improved for samples with higher deposition temperature. Occasional defects are found on the surface of the ZnO layer which can locally alter reflectivity and absorption properties of these solar cells. Despite the high CIGS surface roughness, the CdS layer with an average thickness of only 50 nm appears continuous and even fills trenches between CIGS grains near the interface.
Interfaces in CdTe Solar Cells: From Idealized Concepts to Technology
Authors: Jaegermann Wolfram , Klein Andreas , Fritsche Jochen , Kraft Daniel , Späth Bettina 
Published: November 2011

AbstractIn thin film solar cells interfaces between lattice mismatched or dissimilar materials are used for the front and the back contact. A p-i-n device structure should be possible as most simple but ideally suited thin film solar cell. In contrast the interfaces in CdTe solar cells are found to be much more complex containing interdiffused phase boundaries at the front as well as at the back contact. By comparison to non-interdiffused interfaces using contact phases of adapted work functions it can be shown that the contact potentials of the front contact but also of the back contact are dominated by Fermi level pinning. The pinning states are evidently due to dislocation defects at the boundary of CdTe to the contact phases. Based on these results it is concluded that interdiffused phase boundaries or appropriate passivation layers are a precondition for efficient solar cells whenever strongly lattice mismatched or dissimilar materials are combined.
Transparent Conducting Oxide Sculptured Thin Films for Photovoltaic Applications
Authors: Podraza N. J. , Chen Chi , Sainju D. , Ezekoye O. , Horn M. W. , Wronski C. R. , Collins R. W. 
Published: November 2011

AbstractOptical losses in thin film solar cells arise due to reflections at the top interfaces where dielectric discontinuities may be significant, e.g., between the glass and transparent conducting oxide (TCO) contact and between the TCO and semiconductor structure. Advanced optical engineering approaches are needed to minimize such losses. One approach is to incorporate multilayered or graded-index TCO films designed to act as broad-band anti-reflectors. Thus, it is important to be able to modulate the near-infrared/visible index of refraction of the TCO over a relatively wide range (e.g., 1.3 < n < 2.0) without increasing its extinction coefficient k or significantly degrading its electrical conductance. Here we report an investigation of SnO2 and ZnO sculptured thin films (STFs) under development for this purpose Sculptured thin films are deposited under low surface mobility conditions using stepwise or continuous variations in the polar and/or azimuthal angles of the deposition flux impinging on the surface. Deposition at a glancing polar angle leads to columnar growth, optical anisotropy, and low ordinary indices of refraction, whereas normal incidence deposition under the same conditions leads to dense isotropic films and high indices. In this study, we explore the dependence of the optical properties of SnO2 and ZnO, including index and birefringence spectra, on the polar deposition angle. Optical modeling reported here assesses the ability of the STF concept to provide tailored TCOs for advanced optical engineering of CdTe solar cell structures.
Dependence of the MoSe2 Formation on the Mo Orientation and the Na Concentration for Cu(In,Ga)Se2 Thin-Film Solar Cells
Authors: Abou-Ras Daniel , Mukherji Debashis , Kostorz Gernot , Brémaud David , Kälin Marc , Rudmann Dominik , Döbeli Max , Tiwari Ayodhya N. 
Published: November 2011

AbstractThe formation of MoSe2 has been studied on polycrystalline Mo layers and on Mo single crystals in dependence of the Mo orientation, the Na concentration, and also as a function of the Se source and the substrate temperatures. The Mo substrates were selenized by evaporation of Se. The samples were analyzed by means of X-ray diffraction, Rutherford backscattering spectrometry, elastic recoil detection analysis, and by conventional and high-resolution transmission electron microscopy. It was found that the crystal structure and orientation of the MoSe2 layer change with increasing substrate temperature. However, the texture of MoSe2 does not depend on the orientation of the Mo substrate. It was also found that the MoSe2 growth is significantly influenced by the Na concentration at substrate temperatures of 450°C and 580°C.
Roles of the NFκB and glutathione pathways in mature human erythrocytes
Authors: Ghashghaeinia Mehrdad , Toulany Mahmoud , Saki Mohammad , Rodemann H. , Mrowietz Ulrich , Lang Florian , Wieder Thomas 
Published: November 2011

AbstractAnucleated erythrocytes were long considered as oxygen-transporting cells with limited regulatory functions. Components of different nuclear signaling pathways have not been investigated in those cells, yet. Surprisingly, we repeatedly found significant amounts of transcription factors in purified erythrocyte preparations, i.e. nuclear factor κB (NFκB), and major components of the canonical NFκB signaling pathway. To investigate the functional role of NFκB signaling, the effects of the preclinical compounds Bay 11-7082 and parthenolide on the survival of highly purified erythrocytes were investigated. Interestingly, both inhibitors of the NFκB pathway triggered erythrocyte programmed cell death as demonstrated by enhanced phospholipid scrambling (phosphatidylserine exposure) and cell shrinkage. Anucleated erythrocytes are an ideal cellular model allowing the study of nongenomic mechanisms contributing to suicidal cell death. As NFκB inhibitors might also interfere with the anti-oxidative defense systems of the cell, we measured the levels of reduced glutathione (GSH) after challenge with the inhibitors. Indeed, incubation of erythrocytes with Bay 11-7082 clearly decreased erythrocyte GSH levels. In conclusion, the pharmacological inhibitors of the NFκB pathway Bay 11-7082 and parthenolide interfere with the survival of erythrocytes involving mechanisms other than disruption of NFκB-dependent gene expression. Besides affecting erythrocyte survival, NFκB inhibition and induction of erythrocyte phosphatidylserine exposure may influence blood clotting. Future studies will be aimed at discriminating between NFκB-dependent and NFκB-independent GSH-mediated effects of Bay 11-7082 and parthenolide on erythrocyte death.
Dynamic traffic assignment: model classifications and recent advances in travel choice principles
Authors: Szeto W. , Wong S. 
Published: November 2011

Abstract
Dynamic Traffic Assignment (DTA) has been studied for more than four decades and numerous reviews of this research area have been conducted. This review focuses on the travel choice principle and the classification of DTA models, and is supplementary to the existing reviews. The implications of the travel choice principle for the existence and uniqueness of DTA solutions are discussed, and the interrelation between the travel choice principle and the traffic flow component is explained using the nonlinear complementarity problem, the variational inequality problem, the mathematical programming problem, and the fixed point problem formulations. This paper also points out that all of the reviewed travel choice principles are extended from those used in static traffic assignment. There are also many classifications of DTA models, in which each classification addresses one aspect of DTA modeling. Finally, some future research directions are identified.