Electronic defect study on low temperature processed Cu(In,Ga)Se2 thin-film solar cells and the influence of an Sb layer

A way to lower the manufacturing cost of Cu(In,Ga)Se-2 (CIGS) thin-film solar cells is to use flexible polymer substrates instead of rigid glass. Because such substrates require lower temperature during absorber deposition, the grain growth of the absorber layer can be hindered which leads to a lower cell performance. Partial compensation of this efficiency loss might be accomplished by growing the absorber in the presence of Sb, which is reported to promote grain growth. In this work CIGS solar cells, deposited on glass substrates, at a reduced substrate temperature with a thin Sb layer (7, 12 nm) on top of the Mo contact are investigated. The diffusion profile of Sb is measured with plasma profiling time of flight mass spectrometry. The beneficial effect of Sb on efficiency and grain size is shown in quantum efficiency measurements and with scanning electron microscopy, respectively. Electric spectroscopy is used to explore the possible effects on the defect structure, more in particular on the dominant shallow acceptor. Admittance spectra exhibit a capacitance step to the geometric capacitance plateau at low temperature (5-60 K). Analyzing this capacitance step, we obtained a good estimate of the activation energy of the intrinsic defects that provide the p-type conductivity of the CIGS absorber. The measurements did not show a change in the nature of the dominant acceptor upon Sb treatment

Detection of negative ions in glow discharge mass spectrometry for analysis of solid specimens

A new method is presented for elemental and molecular analysis of halogen-containing samples by glow discharge time-of-flight mass spectrometry, consisting of detection of negative ions from a pulsed RF glow discharge in argon. Analyte signals are mainly extracted from the afterglow regime of the discharge, where the cross section for electron attachment increases. The formation of negative ions from sputtering of metals and metal oxides is compared with that for positive ions. It is shown that the negative ion signals of F(-) and TaO(2)F(-) are enhanced relative to positive ion signals and can be used to study the distribution of a tantalum fluoride layer within the anodized tantala layer. Further, comparison is made with data obtained using glow-discharge optical emission spectroscopy, where elemental fluorine can only be detected using a neon plasma. The ionization mechanisms responsible for the formation of negative ions in glow discharge time-of-flight mass spectrometry are briefly discussed

Chemical analysis of Cd12xZnxS/CdTe solar cells by plasma profiling TOFMS

Thin film CdTe photovoltaic (PV) devices and reference layers obtained by the atmospheric pressure metalorganic vapour deposition (AP-MOCVD) method have been studied for their chemical structure using plasma profiling time-of-flight-mass spectroscopy (PP-TOFMS, also called glow discharge TOFMS). Different levels of arsenic (As) dopant in CdTe films were measured by PP-TOFMS and compared to results obtained from a more conventional depth profiling method (secondary ion mass spectrometry or SIMS). This comparison showed that PPTOFMS has the sufficient sensitivity towards detection of the As dopant in CdTe and hence is suited as a rapid, low vacuum tool in controlling the large scale production of CdTe PV materials

Direct chemical in-depth profile analysis and thickness quantification of nanometer multilayers using pulsed-rf-GD-TOFMS

7 páginas, 3 figuras, 2 tablas.Nanometer depth resolution is investigated using an innovative pulsed-radiofrequency glow discharge time-of-flight mass spectrometer (pulsed-rf-GD-TOFMS). A series of ultra-thin (in nanometers approximately) Al/Nb bilayers, deposited on Si wafers by dc-magnetron sputtering, is analyzed. An Al layer is first deposited on the Si substrate with controlled and different values of the layer thickness, t Al. Samples with t Al = 50, 20, 5, 2, and 1 nm have been prepared. Then, a Nb layer is deposited on top of the Al one, with a thickness t Nb = 50 nm that is kept constant along the whole series. Qualitative depth profiles of those layered sandwich-type samples are determined using our pulsed-rf-GD-TOFMS set-up, which demonstrated to be able to detect and measure ultra-thin layers (even of 1 nm). Moreover, Gaussian fitting of the internal Al layer depth profile is used here to obtain a calibration curve, allowing thickness estimation of such nanometer layers. In addition, the useful yield (estimation of the number of detected ions per sputtered atom) of the employed pulsed-rf-GD-TOFMS system is evaluated for Al at the selected operating conditions, which are optimized for the in-depth profile analysis with high depth resolution.This work is supported by the European Union 6th framework program within the EMDPA project (contract No 032202 (NMP3-CT-2006-032202)) and by Spanish Ministry of Science (grant No MAT2007-65097-C02 and FIS2008-06249). R. Valledor acknowledges financial support from FPU Ph.D. Grant from Ministry of Education of Spain. Additionally, J. Pisonero and C. Quiros acknowledge financial support from “Ramon y Cajal” Research Program of the Ministry of Education of Spain, cofinanced by the European Social Fund.Peer reviewe

Imaging Mass Spectrometry: Hype or Hope?

Imaging mass spectrometry is currently receiving a significant amount of attention in the mass spectrometric community. It offers the potential of direct examination of biomolecular patterns from cells and tissue. This makes it a seemingly ideal tool for biomedical diagnostics and molecular histology. It is able to generate beautiful molecular images from a large variety of surfaces, ranging from cancer tissue sections to polished cross sections from old-master paintings. What are the parameters that define and control the implications, challenges, opportunities, and (im)possibilities associated with the application of imaging MS to biomedical tissue studies. Is this just another technological hype or does it really offer the hope to gain new insights in molecular processes in living tissue? In this critical insight this question is addressed through the discussion of a number of aspects of MS imaging technology and sample preparation that strongly determine the outcome of imaging MS experiments

Dendritic Cells Crosspresent Antigens from Live B16 Cells More Efficiently than from Apoptotic Cells and Protect from Melanoma in a Therapeutic Model

Dendritic cells (DC) are able to elicit anti-tumoral CD8+ T cell responses by cross-presenting exogenous antigens in association with major histocompatibility complex (MHC) class I molecules. Therefore they are crucial actors in cell-based cancer immunotherapy. Although apoptotic cells are usually considered to be the best source of antigens, live cells are also able to provide antigens for cross-presentation by DC. We have recently shown that prophylactic immunotherapy by DC after capture of antigens from live B16 melanoma cells induced strong CD8+ T-cell responses and protection against a lethal tumor challenge in vivo in C57Bl/6 mice. Here, we showed that DC cross-presenting antigens from live B16 cells can also inhibit melanoma lung dissemination in a therapeutic protocol in mice. DC were first incubated with live tumor cells for antigen uptake and processing, then purified and irradiated for safety prior to injection. This treatment induced stronger tumor-specific CD8+ T-cell responses than treatment by DC cross-presenting antigens from apoptotic cells. Apoptotic B16 cells induced more IL-10 secretion by DC than live B16 cells. They underwent strong native antigen degradation and led to the expression of fewer MHC class I/epitope complexes on the surface of DC than live cells. Therefore, the possibility to use live cells as sources of tumor antigens must be taken into account to improve the efficiency of cancer immunotherapy

Quantitative depth profile analysis of boron implanted silicon by pulsed radiofrequency glow discharge time-of-flight mass spectrometry

a b s t r a c t The analytical potential of pulsed radiofrequency glow discharge time-of-flight mass spectrometry (pulsed-rf-GD-TOFMS) is investigated for fast quantitative analysis of major and dopant elements in bulk and thin film layers. This technique does not require sampling at ultra-high vacuum conditions and so it facilitates high sample throughput compared to reference techniques as secondary ionization mass spectrometry (SIMS). In this paper, bulk and boron implanted silicon samples are analyzed. Boron concentration in Si samples is calculated from calibration curves obtained using solar grade silicon and B doped silicon wafers as calibrating materials, and using 29 Si + ion signal as internal standard. Qualitative depth profiles of 10 B implanted silicon are determined in a few seconds using the lowpressure pulsed-rf-GD-TOFMS system. Additionally, quantitative depth profiles are easily determined making use of the calibration curves. A good agreement with the depth profiles measured using SIMS was obtained, demonstrating the analytical potential of the pulsed-GD-TOFMS system for fast, sensitive and high depth resolution analysis of implanted silicon samples