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This contribution reports on surface photovoltage SPV investigations of wet chemical substrate treatments in hydrochloric acid HCl and hydrofluoric acid HF containing DIW O3 solutions, which were developed in order to reduce the number of wet chemical process steps, by combination of cleaning, oxidation and etching processes in the same bath. According to our earlier reported results, after sequences of DIW O3 oxidation and subsequent oxide removal in diluted HF solution on H terminated substrates values of interface states densities Dit,min lt; 5 amp; 8729; 1011eV 1cm 2 could be achieved, comparable to values obtained on similar substrates by the standard RCA process followed by HF dip. it is demonstrated, that field depending SPV measurement can be used as a surface sensitive tool to investigate and optimize wet chemical Si surface treatments with O3 containing solutions. Oxidizing treatments in DIW O3 with HCl admixture can be utilized for passivation of substrate surfaces by well defined wet chemical oxide layers as utilized for tunnel oxide passivated contacts TOPCon . Furthermore, depending on the O3, HCl and HF content H terminated substrate surfaces can be prepared as starting point of subsequent PECVD deposition processes for high efficiency silicon Heterojunctions

Hypomethylating agents are able to prolong the overall survival of some patients diagnosed with acute myeloid leukemia. The aim of this study was to evaluate the clinical use of azacitidine as front-line therapy in unfit acute myeloid leukemia (AML) patients and to develop a clinical prediction model to identify which patients may benefit more from the drug. One hundred and ten untreated unfit AML patients received front-line azacitidine therapy in Spain, and response and survival were evaluated in them following European LeukemiaNet (ELN) guidelines. A clinical prediction rule was obtained from this population that was validated and refined in 261 patients treated in France, Austria and Italy. ELN response was achieved in 21.0% of the 371 patients (CI95% 17.0-25.5) and did not depend on bone marrow blast cell percentage. Median overall survival was 9.6 months (CI95% 8.5-10.8) and 40.6% of the patients were alive at 1 year (CI95% 35.5-45.7). European ALMA score (E-ALMA), based on performance status, white blood cell counts at azacitidine onset and cytogenetics, discriminated three risk groups with different survival and response rates. Azacitidine seems a reasonable therapeutic option for most unfit AML patients, i.e. those displaying a favorable or intermediate E-ALMA score. © 2014 Elsevier Ltd.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1093-1098, A systematic step by step comparison of amorphous/crystalline heterojunction (a-Si:H/c-Si) solar cells textured in isopropanol(IPA)-free KOH solution and in IPA-containing KOH solution was performed in order to investigate the potential and limitations of IPA-free solar cell processing for reaching high efficiencies. As a result, a- Si:H/c-Si solar cells on n-type substrate, textured in IPA-free solution and in IPA-containing solution, both with conversion efficiencies exceeding 20 % are obtained. These values represent a considerable improvement over our previously reported best cell efficiencies for cells with a-Si:H(i) buffer layer. They were achieved by thorough optimization of the surface texture, the pyramid morphology, and the a-Si:H/c-Si interface passivation, resulting in improved open-circuit voltages and fill factors. Thus, solar cells fabricated on IPA-free textured wafers can compete with those processed on wafers textured in conventional IPA-containing alkaline solution and are an attractive alternative for industrial production due to their better process control, lower replenishments and lower costs.

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27th European Photovoltaic Solar Energy Conference and Exhibition; 547-551, Different wet-chemical treatments of crystalline Si wafers for the preparation of heterojunction solar cells are optimized with respect to low reflection losses, low recombination losses and long carrier lifetimes. It is demonstrated that a joint optimization of both saw damage etch and texture etch is necessary to control the pyramid morphology. Best results are reached for intermediate saw damage removals and texture etch times. Wet-chemical preconditioning by oxidation in hot water and by using ozone at ambient temperatures is found to yield high-quality surfaces with low defect densities. These methods are considered as low-cost alternatives to conventional approaches. The surface photovoltage (SPV) technique is established as efficient tool for technology optimization and allows a fast and reliable interface characterization and the quantitative determination of interface defect densities.

27th European Photovoltaic Solar Energy Conference and Exhibition; 888-895, The interface passivation of a-AlOx/a-SiNx:H stacks deposited on p-type silicon by in-line plasma enhanced chemical vapor deposition is investigated by means of charge carrier lifetime, field dependent surface photovoltage and capacitance voltage measurements as well as Fourier transform infrared spectroscopy. To control the quality of the interface, we performed different wet chemical surface preparation steps prior to a-AlOx/a-SiNx:H stack deposition. Our investigation is focusing on the interface passivation upon post-deposition thermal treatments such as annealing at 425 °C and firing at 860 °C as applied in the silicon solar cell industry. We demonstrate that the interface recombination is mainly controlled by the interface state density as demonstrated by the correlation between the surface recombination velocity and interface state density inferred from lifetime and SPV measurements. The increase of the negative charge density after thermal steps as revealed by capacitance-voltage measurements correlates with the increase of the density of negatively charged AlO4 tetrahedra as revealed by infrared spectroscopy suggesting that the tetrahedrally coordinated Al contribute to the formation of the negative charge.

LGEP 2011 ID = 884

26th European Photovoltaic Solar Energy Conference and Exhibition; 1593-1597, The combination of fast, non-destructive, and surface sensitive spectroscopic methods, i.e. pulsed field-modulated surface photovoltage (SPV) and quasi-steady-state photo conductance (QSSPC), provided detailed information about the influence of wet-chemical substrate preparation methods on the surface charge, energetic distribution of interfaces states Dit(E) on solar cell substrates and the resulting interface recombination losses on subsequent prepared ultra-thin passivation layers. The SPV technique allows the measurement of the surface potential and determination of the interface state densities without any contact preparation. The results of these investigations could be successfully used to enhance the electronic properties of polished, saw damage etched and textured solar cell substrates with random pyramids by wetchemical smoothing and H-termination procedures. As demonstrated for selected examples, this favourable effect can be preserved during the subsequent oxidation by thermalized atomic oxygen or during the soft plasma enhanced chemical vapor deposition (PECVD) of amorphous silicon (a-Si:H). The resulting Dit(E) on ultra-thin Si/SiO2 layers and interface recombination losses on a-Si:H/c-Si hetero-junctions were found to be significantly reduced compared to the standard RCA pre-treatment.

26th European Photovoltaic Solar Energy Conference and Exhibition; 839-842, Treatment of crystalline silicon solar cells with ozone dissolved in ultra pure water is a low cost alternative to improve surface characteristics before and after emitter formation. The impact of dissolved ozone treatment after texturing has been investigated with respect to interface state densities and the possibility of improving the emitter formation with a low cost process enhancement. The chemically grown thin oxide improves wetting capability without modification of other surface characteristics that can impact cell efficiency. It could be shown that already low concentrations of ozone in UPW prior to phosphorus doping improves sheet resistance uniformity on Cz-Si and multi-crystalline Si solar cells by 30-50%.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1954-1957, The relations between light trapping behavior, structural imperfections, energetic distribution of interface state densities and interface recombination losses were investigated on as-cut, saw damage etched and textured mono-crystalline silicon substrates for solar cell manufacturing. Surface sensitive techniques, the field-modulated surface photovoltage (SPV), total hemispherical UV-NIR-reflectance measurements and electron microscopy (SEM) were employed to yield detailed information on the influence of wet-chemical treatments on preparation induced texture, nano-roughness and electronic properties of polished and textured silicon substrates. The correlation between UV reflectance and SPV measured surface state-density has been investigated. As a result, the different contributions of micron-sized texture and nanometer-sized surface roughness to the reflectance signal have been separated and a measurement set-up and optical model for routine evaluation of wet-chemical surface texturization in production processes has been established.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1640-1644, We have performed a systematic variation of the wet chemical oxidation and the subsequent oxide etching steps during the cleaning of Czochralski (CZ) single crystalline silicon wafers prior to surface passivation. The optimization of these preconditioning steps was carried out on saw-damage etched or textured Si wafers subsequently passivated by amorphous silicon nitride (a-SiNx:H) or chemical passivation by an iodine ethanol (I/E) solution. Measuring the carrier lifetime using the spatially resolved microwave detected photoconductance decay, we monitored the impact of the wet-chemical surface conditioning on the surface morphology and wafer base doping type. For damage etched surfaces in alkaline potassium oxide solutions and passivated by iodine ethanol, an optimum surface passivation is obtained by omitting the last water rinse (as used in the standard clean) and adding a hot water treatment as final step in the cleaning procedure. While this results was found for both p-type and n-type wafers, suggesting that the passivation mechanism is based on the saturation of dangling bonds, a strong dependence on the doping type was observed for the passivation by a-SiNx:H. Prior to passivation by a-SiNx:H, the best preconditioning for n-type was achieved by adding a hot water treatment and subsequent etching of the oxide by hydrofluoric acid (HF). For p-type however, no improvement was achieved with respect to the standard cleaning step. This dependency on the base doping type could be attributed to the passivation mechanism of a-SiNx:H based on the field effect. By employing ammonium fluoride as final etching solution instead HF, followed by hot water treatment, compared to the standard treatment, an improvement of the lifetime can be observed for both surface structures, indicating that the surface micro-roughness can be reduced and the contamination can be removed.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1422-1426, Combined in-situ PL and ex-situ SPV measurements were applied to optimize treatment times for wet-chemical etching processes for textured Silicon substrates. Applying smoothing procedures with extended HF treatment times, a definitive oxide removal was achieved. Two complementary strategies to enhance the electronic properties of (p)a-Si:H/(n)c-Si interfaces - wet-chemical substrate pre-treatment before a-Si:H deposition and the inclusion of intrinsic a-Si:H buffer layers - are discussed and their effect on the carrier lifetime, FF and open circuit voltage is explored. It was shown that the combination of special wet-chemical substrate pre-treatments and deposition of an intrinsic buffer layer at the a-Si:H/c-Si interface, shown previously to increase cell performance in (n)a-Si:H/(p)c-Si structures [1], can also be utilized to optimizes interface properties for the inverse structure, i.e. (p)a-Si:H/(n)c-Si hetero-junction solar cells.