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1.
Reactive Magnetron Sputtering of Thin Film Solar Cells We show that reactive magnetron sputtering is well suited to deposit CuInS2‐thin film absorber layers of high electronic quality. Using metallic targets and substrate temperatures below 500 °C, compact films with grain sizes in the micrometer range can be obtained. The structural and electronic properties of these layers are comparable to CuInS2 thin films prepared by a 2‐step sulfurization process, which is being commercialized at present. In particular, the reactively sputtered films show minority carrier diffusion lengths larger than the layer thickness (≈ 2μm). This results in solar cells with conversion efficiences larger than 10 %, comparable to the best conversion efficiencies for CuInS2‐solar cells obtained from other deposition processes. These results are promising for the potential application of magnetron sputtering as a large area deposition process for absorber layers in thin film solar cells. 相似文献
2.
Wolfram Witte Daniel Abou‐Ras Karsten Albe Gottfried H. Bauer Frank Bertram Christian Boit Rudolf Brüggemann Jürgen Christen Jens Dietrich Axel Eicke Dimitrios Hariskos Matthias Maiberg Roland Mainz Max Meessen Mathias Müller Oliver Neumann Thomas Orgis Stefan Paetel Johan Pohl Humberto Rodriguez‐Alvarez Roland Scheer Hans‐Werner Schock Thomas Unold Alfons Weber Michael Powalla 《Progress in Photovoltaics: Research and Applications》2015,23(6):717-733
The gallium gradient in Cu(In,Ga)Se2 (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co‐evaporation processes, plays a key role in the device performance of CIGS thin‐film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X‐ray measurements. In addition, the gallium grading of a CIGS layer grown with an in‐line co‐evaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth‐dependent occurrence of lateral inhomogeneities on the µm scale in CIGS deposited by the co‐evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi‐Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross‐sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper‐vacancy‐mediated indium and gallium diffusion in CuInSe2 and CuGaSe2 were calculated using density functional theory. The migration barrier for the InCu antisite in CuGaSe2 is significantly lower compared with the GaCu antisite in CuInSe2, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co‐evaporation and selenization processes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
Effect of copper-deficiency on multi-stage co-evaporated Cu(In,Ga)S2 absorber layers and solar cells
B. Marsen H. WilhelmL. Steinkopf S. KlemzT. Unold R. ScheerH.-W. Schock 《Thin solid films》2011,519(21):7224-7227
Solar cell absorber films of Cu(In,Ga)S2 have been fabricated by multi-stage co-evaporation resulting in compositional ratios [Cu]/([In] + [Ga]) = 0.93-0.99 and [Ga]/([In] + [Ga]) = 0.15. Intentional doping is provided by sodium supplied from NaF precursor layers of different thicknesses. Phases, structure and morphology of the resulting films are investigated by X-ray diffraction (XRD) and scanning electron microscopy. The XRD patterns show CuIn5S8 thiospinel formation predominantly at the surface in order to accommodate decreasing Cu content. Correlated with the CuIn5S8 formation, a Ga-enrichment of the chalcopyrite phase is seen at the surface. Since no CuS layer is present on the as-deposited films, functioning solar cells with CdS buffer and ZnO window layers were fabricated without KCN etch. The open-circuit voltage of solar cells correlates with the copper content and with the amount of sodium supplied. The highest efficiency cell (open-circuit voltage 738 mV, short-circuit current 19.3 mA/cm2, fill factor 65%, efficiency 9.3%) is based on the absorber with the least Cu deficiency, [Cu]/([In] + [Ga]) = 0.99. The activation energy of the diode saturation current density of such a cell is extracted from temperature- and illumination-dependent current-voltage measurements. A value of 1.04 eV, less than the band gap, suggests the heterojunction interface as the dominant recombination zone, just as in cells based on Cu-rich grown Cu(In,Ga)S2. 相似文献
4.
U Beyer T Roth P Schumacher G Maier A Unold AW Frahm HH Fiebig C Unger F Kratz 《Canadian Metallurgical Quarterly》1998,41(15):2701-2708
One strategy for improving the selectivity and toxicity profile of antitumor agents is to design drug carrier systems employing soluble macromolecules or carrier proteins. Thus, five maleimide derivatives of chlorambucil were bound to thiolated human serum transferrin which differ in the stability of the chemical link between drug and spacer. The maleimide ester derivatives 1 and 2 were prepared by reacting 2-hydroxyethylmaleimide or 3-maleimidophenol with the carboxyl group of chlorambucil, and the carboxylic hydrazone derivatives 5-7 were obtained through reaction of 2-maleimidoacetaldehyde, 3-maleimidoacetophenone, or 3-maleimidobenzaldehyde with the carboxylic acid hydrazide derivative of chlorambucil. The alkylating activity of transferrin-bound chlorambucil was determined with the aid of 4-(4-nitrobenzyl)pyridine (NBP) demonstrating that on average 3 equivalents were protein-bound. Evaluation of the cytotoxicity of free chlorambucil and the respective transferrin conjugates in the MCF7 mammary carcinoma and MOLT4 leukemia cell line employing a propidium iodide fluorescence assay demonstrated that the conjugates in which chlorambucil was bound to transferrin through non-acid-sensitive linkers, i.e., an ester or benzaldehyde carboxylic hydrazone bond, were not, on the whole, as active as chlorambucil. In contrast, the two conjugates in which chlorambucil was bound to transferrin through acid-sensitive carboxylic hydrazone bonds were as active as or more active than chlorambucil in both cell lines. Especially, the conjugate in which chlorambucil was bound to transferrin through an acetaldehyde carboxylic hydrazone bond exhibited IC50 values which were approximately 3-18-fold lower than those of chlorambucil. Preliminary toxicity studies in mice showed that this conjugate can be administered at higher doses in comparison to unbound chlorambucil. The structure-activity relationships of the transferrin conjugates are discussed with respect to their pH-dependent acid sensitivity, their serum stability, and their cytotoxicity. 相似文献
5.
Eitan Oksenberg Calvin Fai Ivan G. Scheblykin Ernesto Joselevich Eva L. Unger Thomas Unold Charles Hages Aboma Merdasa 《Advanced functional materials》2021,31(22):2010704
Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr3 nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr3 nanowires, an ambipolar carrier mobility of μ = 35 cm2 V−1 s−1 is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL. 相似文献
6.
T. Eisenbarth T. Unold R. Caballero C.A. Kaufmann D. Abou-Ras H.-W. Schock 《Thin solid films》2009,517(7):2244-7316
A series of CuIn1 − xGaxSe2 solar cells with varied Ga content (0 ≤ x ≤ 1) was prepared using a three-stage co-evaporation process. The grain sizes of these devices vary with gallium content, exhibiting a maximum for approximately x = 0.2, which does not coincide with the maximum of the solar conversion efficiency observed between 0.34 < x < 0.37 for these devices.Admittance spectroscopy and drive-level capacitance profiling measurements were performed yielding a defect level with an activation energy of Ea = 0.1 eV which is independent of the amount of Ga and the grain size respectively. This defect closely resembles the N1 defect level reported in the literature. Only for relatively high Ga contents (x > 0.7) an additional defect appears. An equivalent circuit model describing a parallel connection of bulk and grain boundary capacitors allows us to conclude that the detected shallow defect is not predominantly located at the grain boundaries. 相似文献
7.
Unold J. Golling M. Mederer F. Michalzik R. Supper D. Ebeling K.J. 《Electronics letters》2001,37(9):570-572
Completely singlemode MBE-grown selectively oxidised InGaAs-VCSELs with aperture diameters of up to 14 μm have been fabricated using a self-aligned shallow surface etch. By choosing the growth position accordingly, a continuous variation of the aperture diameter across the wafer is achieved to optimise the surface etch to aperture diameter ratio. A record singlemode output power of 5.7 mW (30 dB SMSR) is obtained for a 5.8 μm-aperture diameter, 2.8 μm etch spot diameter device 相似文献
8.
C.A. Kaufmann R. Caballero T. Unold R. Hesse R. Klenk S. Schorr M. Nichterwitz H.-W. Schock 《Solar Energy Materials & Solar Cells》2009,93(6-7):859-863
In order to understand the effect of the process temperature on the growth of Cu(In,Ga)Se2 (CIGSe) thin films via the 3-stage co-evaporation process, absorber layers have been fabricated on glass using a set of different maximum process temperatures in the nominal temperature range between 330 and 525 °C. Using energy dispersive X-ray analysis, depth profiles could be recorded on cross-sections of finished devices and were correlated to the device performance. The effect of the process temperature on the gallium gradient in the CIGSe layer is evident in the gallium distribution across the depth of the device. 相似文献
9.
Florian Unold 《Bautechnik》2009,86(12):765-773
Es wird ein Berechnungsmodell zur quantitativen Bestimmung der Netto‐Tausetzung sowie der Druck‐Porenzahl‐Beziehung bei Weiterbelastung nach dem Auftauen feinkörniger Böden vorgestellt. Der Ansatz berücksichtigt die Inhomogenität der Veränderung des Bodengefüges infolge der Vereisung. Hierbei wird der Boden vereinfachend in zwei Bereiche unterteilt. Nach dem Modell wird ein Teil des Bodens mit einer rechnerischen Auflast, die der Summe der komprimierenden Vorgänge während der Bodenvereisung äquivalent ist, verdichtet. Für den übrigen Teil wird angenommen, dass er von der Vereisung unbeeinflusst bleibt. Die mit Hilfe des Modells ermittelten Berechnungsergebnisse stehen in sehr guter Übereinstimmung mit den Versuchsergebnissen. Der große Vorteil des Berechnungsansatzes liegt darin, dass eine zuverlässige Prognose der Kompressionseigenschaften des aufgetauten Bodens allein mit den Ergebnissen von Standard‐Laborversuchen möglich ist. A model for the estimation of the thaw‐settlements and the compressibility properties of thawed soils. A mathematical model is presented which allows the quantitative calculation of the net thaw‐settlement as well as of the pressure‐void ratio relation at continued loading of fine grained soils after thawing. The approach takes into account the inhomogeneity of the change of the soil fabric caused by freezing. For this purpose, the soil is being divided into two parts, which is a simplification of the real situation. In the model, one part of the soil is being compacted with a load that is equivalent to the sum of all compressing processes during ground freezing. For the rest of the soil, it is assumed that it remains unaffected by freezing. The calculation results obtained by the model show good agreement with the results of laboratory tests. The great advantage of the introduced approach is that the compression properties of thawed soil can be reliably predicted just based on the results of standard laboratory tests. 相似文献
10.
Arteaga M.A. Unold H.J. Ostermann J.M. Michalzik R. Thienpont H. Panajotov K. 《Quantum Electronics, IEEE Journal of》2006,42(2):102-107
The effect of isotropic optical feedback from an extremely short external cavity on the emission properties of vertical-cavity surface-emitting lasers (VCSELs) is experimentally investigated. When changing the external cavity length a modulation of the total power and the wavelength emitted by the VCSEL is observed with a period of half the wavelength of operation of the device. When biasing the VCSEL around its solitary (without optical feedback) polarization switching (PS) current, PS between the two linearly polarized modes is observed by changing the external cavity length. This PS is found to occur through a hysteresis region. Our experimental results show a modulation of the PS currents and the hysteresis width when changing the external cavity length with a period of half the wavelength of operation. The experimental results are well explained by a two mode rate equation model. 相似文献