On the determination of the interface density of states in a-Si:H/a-SiC:H multilayers

This paper deals with the determination of the interface density of states in amorphous silicon-based multilayers. Photothermal deflection spectroscopy is used to characterize two series of aSi:H/aSi1-xCx:H multilayers, and a new approach in the treatment of experimental dada is used in order to obtain accurate results. From this approach, an upper limit of 10^10 cm-2 is determined for the interface density of states

Substrate influence on the properties of doped thin silicon layers grown by Cat-CVD

We present structural and electrical properties for p- and n-type layers grown close to the transition between a-Si:H and nc-Si:H onto different substrates: Corning 1737 glass, ZnO:Al-coated glass and stainless steel. Structural properties were observed to depend on the substrate properties for samples grown under the same deposition conditions. Different behaviour was observed for n- and p-type material. Stainless steel seemed to enhance crystallinity when dealing with n-type layers, whereas an increased crystalline fraction was obtained on glass for p-type samples. Electrical conduction in the direction perpendicular to the substrate seemed to be mainly determined by the interfaces or by the existence of an amorphous incubation layer that might determine the electrical behaviour. In the direction perpendicular to the substrate, n-type layers exhibited a lower resistance value than p-type ones, showing better contact properties between the layer and the substrate

Optical analysis of textured plastic substrates to be used in thin silicon solar cells

Light confinement strategies in thin-film silicon solar cells play a crucial role in the performance of the devices. In this work, the possible use of Ag-coated stamped polymers as reflectors to be used in n-i-p solar cells is studied. Different random roughnesses (nanometer and micrometer size) have been transferred on poly(methylmethacrylate) (PMMA) by hot embossing. Morphological and optical analyses of masters, stamped polymers and reflectors have been carried out evidencing a positive surface transference on the polymer and the viability of a further application in solar cells

Control of doped layers in p-i-n microcrystalline solar cells fully deposited with HWCVD

In this paper, the influence of the deposition conditions on the performance of p-i-n microcrystalline silicon solar cells completely deposited by hot-wire chemical vapor deposition is studied. With this aim, the role of the doping concentration, the substrate temperature of the p-type layer and of amorphous silicon buffer layers between the p/i and i/n microcrystalline layers is investigated. Best results are found when the p-type layer is deposited at a substrate temperature of 125 °C. The dependence seen of the cell performance on the thickness of the i layer evidenced that the efficiency of our devices is still limited by the recombination within this layer, which is probably due to the charge of donor centers most likely related to oxygen

Progress in single junction microcrystalline silicon solar cells deposited by Hot-Wire CVD

Hot-Wire Chemical Vapor Deposition has led to microcrystalline silicon solar cell efficiencies similar to those obtained with Plasma Enhanced CVD. The light-induced degradation behavior of microcrystalline silicon solar cells critically depends on the properties of their active layer. In the regime close to the transition to amorphous growth (around 60% of amorphous volume fraction), cells incorporating an intrinsic layer with slightly higher crystalline fraction and [220] preferential orientation are stable after more than 7000 h of AM1.5 light soaking. On the contrary, solar cells whose intrinsic layer has a slightly lower crystalline fraction and random or [111] preferential orientation exhibit clear light-induced degradation effects. A revision of the efficiencies of Hot-Wire deposited microcrystalline silicon solar cells is presented and the potential efficiency of this technology is also evaluated

Studies on grain boundaries in nanocrystalline silicon grown by Hot-Wire CVD

The use of a tantalum wire in hot-wire chemical vapour deposition (HWCVD) has allowed the deposition of dense nanocrystalline silicon at low filament temperatures (1550 °C). A transition in the crystalline preferential orientation from (2 2 0) to (1 1 1) was observed around 1700 °C. Transmission electron microscopy (TEM) images, together with secondary ion mass spectrometry (SIMS) measurements, suggested that no oxidation occurred in materials obtained at low filament temperature due to the high density of the tissue surrounding grain boundaries. A greater concentration of SiH 3 radicals formed at these temperatures seemed to be responsible for the higher density

Optimization of KOH etching process to obtain textured substrates suitable for heterojunction solar cells fabricated by HWCVD

In this work, we have studied the texturization process of (100) c-Si wafers using a low concentration potassium hydroxide solution in order to obtain good quality textured wafers. The optimization of the etching conditions have led to random but uniform pyramidal structures with good optical properties. Then, symmetric heterojunctions were deposited by Hot-Wire CVD onto these substrates and the Quasi-Steady-State PhotoConductance technique was used to measure passivation quality. Little degradation in the effective lifetime and implicit open circuit voltage of these devices (< 20 mV) was observed in all cases. It is especially remarkable that for big uniform pyramids, the open-circuit voltage is comparable to the values obtained on flat substrates

Light induced defects in thermal annealed hydrogenated amorphous silicon

The metastable defects of a-Si:H samples annealed at temperatures in the 300-550°C range have been studied by photothermal deflection spectroscopy (PDS). The light-soaked samples show an increase in optical absorption in the 0.8 to 1.5 eV range. The metastable defect density decreases when the annealing temperature increases, while the defect density increases. This decrease in the metastable defect density shows an almost linear correlation with the decrease in the hydrogen content of the samples, determined by IR transmission spectroscopy and thermal desorption spectroscopy

Role of age and comorbidities in mortality of patients with infective endocarditis

Purpose: The aim of this study was to analyse the characteristics of patients with IE in three groups of age and to assess the ability of age and the Charlson Comorbidity Index (CCI) to predict mortality. Methods: Prospective cohort study of all patients with IE included in the GAMES Spanish database between 2008 and 2015. Patients were stratified into three age groups:<65 years, 65 to 80 years, and = 80 years.The area under the receiver-operating characteristic (AUROC) curve was calculated to quantify the diagnostic accuracy of the CCI to predict mortality risk. Results: A total of 3120 patients with IE (1327 < 65 years;1291 65-80 years;502 = 80 years) were enrolled.Fever and heart failure were the most common presentations of IE, with no differences among age groups.Patients =80 years who underwent surgery were significantly lower compared with other age groups (14.3%, 65 years; 20.5%, 65-79 years; 31.3%, =80 years). In-hospital mortality was lower in the <65-year group (20.3%, <65 years;30.1%, 65-79 years;34.7%, =80 years;p < 0.001) as well as 1-year mortality (3.2%, <65 years; 5.5%, 65-80 years;7.6%, =80 years; p = 0.003).Independent predictors of mortality were age = 80 years (hazard ratio [HR]:2.78;95% confidence interval [CI]:2.32–3.34), CCI = 3 (HR:1.62; 95% CI:1.39–1.88), and non-performed surgery (HR:1.64;95% CI:11.16–1.58).When the three age groups were compared, the AUROC curve for CCI was significantly larger for patients aged <65 years(p < 0.001) for both in-hospital and 1-year mortality. Conclusion: There were no differences in the clinical presentation of IE between the groups. Age = 80 years, high comorbidity (measured by CCI), and non-performance of surgery were independent predictors of mortality in patients with IE.CCI could help to identify those patients with IE and surgical indication who present a lower risk of in-hospital and 1-year mortality after surgery, especially in the <65-year group