In this paper we report results concerning the effect of the TCO interface on hydrogenated amorphous silicon (a-Si:H) p-i-n homojunction solar cells. Its correlation with dark current density-voltage (J-V) characteristics and spectral response, before and after while light-soaking degradation, is analysed. From this study, we conclude that the properties and stability of these devices are not only influenced by the a-Si:H film properties, but also by the properties of the transparent conductive electrode and its interface with the a-Si:H layer.

n/a

n/a

n/a

n/a

n/a

This paper deals with the engineering aspects related to the rf energy coupling in Plasma Enhanced Chemical Vapour Deposition (PECVD) processes, in a diode-type unit in which an extra grid is used. The main emphasis is given in the determination of the real power delivered to the gas and comparing it with the total power losses, besides determining the best way to control the powder formed during the process. © 1994.

n/a

n/a

Pin solar cells of a-Si:H were light soaked. The cell characteristics, the optoelectronic properties and the microstructure parameter, as well as the hydrogen content and density of states of the i-layer, were monitored throughout the entire light-induced degradation process and compared with the corresponding μτ product (for both carriers) inferred through steady photoconductivity and FST measurements. Results suggest a correlation between the decrease of μτ product for electrons and the increase of the fraction of hydrogen bonded on internal surfaces, showing structural changes during the degradation process. © 1994.

We report experimental data on light soaking of a-Si: H solar cells as well as the role played by the temperature on the metastable light-induced defect growth. We studied the temperature and intensity dependence on the photoconductivity, μτ product and density of states at the Fermi level (g(Ef)) and we found that the rate of defect growth on the i-layer depends on the quality of the material and on the annealing temperature, resulting from an equilibrium between light-induced and light-annealed defects. The photoresponse of the devices is mainly ruled by its microstructure, and depends on the fraction of hydrogen bounded on internal surfaces. Results suggest a correlation between the decrease of μτ product for electron and the increase of the fraction of hydrogen bonded on internal surfaces, suggesting structural changes during the degradation process. Data show, also, that the thermal annealing effect is worthless up to 70°C because of light-induced defect-generation being the dominant process in recombination mechanisms. © 1994.

A [2Fe-2S] cluster has been detected in mammalian ferrochelatase, the terminal enzyme of the heme biosynthetic pathway. Natural ferrochelatase, purified from mouse livers, and recombinant ferrochelatase, purified from an overproducing strain of Escherichia coli, were investigated by electron paramagnetic resonance (EPR) and Mossbauer spectroscopy. In their reduced forms, both the natural and recombinant ferrochelatases exhibited an identical EPR signal with g values (g = 2.00, 1.93, and 1.90) and relaxation properties typical of [2Fe-2S](+) cluster. Mossbauer spectra of the recombinant ferrochelatase, purified from a strain of E. coli cells transformed with a plasmid encoding murine liver ferrochelatase and grown in Fe-57-enriched medium, demonstrated unambiguously that the cluster is a [2Fe-2S] cluster. No change in the cluster oxidation state was observed during catalysis, The putative protein binding site for the Fe-S cluster in mammalian ferrochelatases is absent from the sequences of the bacterial and yeast enzymes, suggesting a possible role of the [2Fe-2S] center in regulation of mammalian ferrochelatases.

n/a

n/a

A evolu{\c c}ão do hardware dos computadores para arquitecturas paralelas, incentivou a concep{\c c}ão de novos modelos de programa{\c c}ão e o desenvolvimento dos sistemas de suporte à execu{\c c}ão correspondentes, de forma a conseguir uma melhor explora{\c c}ão do paralelismo. A linguagem de programa{\c c}ão Prolog, pelas suas caracter\'ısticas declarativas e operacionais, tem vindo a ser objecto de estudo nesta área, através de adapta{\c c}ões da linguagem e/ou da sua máquina de inferência. Este trabalho incide sobre os aspectos de concep{\c c}ão e implementa{\c c}ão de um modelo de um sistema de suporte à execu{\c c}ão de programas em Prolog, em arquitecturas de múltiplos processadores, com unidades de memória fisicamente distribu\'ıdas. O modelo propõe extensões a um executor de Prolog convencional, de forma a disponibilizar funcionalidades que permitam o controlo do paralelismo e da distribui{\c c}ão. Estas funcionalidades podem ser utilizadas para a implementa{\c c}ão de modelos de linguagens lógicas concorrentes de mais alto n\'ıvel, ou então serem utilizadas directamente para a programa{\c c}ão de sistemas distribu\'ıdos, em que múltiplos executores Prolog cooperam na resolu{\c c}ão de um golo, comunicando com base em mensagens. Para avaliar a funcionalidade do modelo proposto, concebeu-se e implementou-se um sistema de distribui{\c c}ão de golos Prolog, que permite recorrer a diversas estratégias para composi{\c c}ão sequencial e paralela de golos, escondendo os aspectos de gestão˜ao expl\'ıcita dos recursos efectivos. A disserta{\c c}ão inclui uma discussão dos aspectos mais relevantes da realiza{\c c}ão do protótipo do modelo proposto sobre uma arquitectura baseada em Transputers.

The introduction into a traditional p.i.n structure of two defective buffer layers near the p/i and i/n interfaces can improve the device stability and efficiency through an enhancement of the electric field profile at the interfaces and a reduction of the available recombination bulk centers. The defectous layer ("i′-layer"), grown at a higher power density, present a high density of defects and acts as "gettering centers" able to tailor light induced defects under degradation conditions. If the i-layer density of states remains below 1016 eV-1 cm-3 and assuming a Gaussian distribution of defect states, the gettering center distribution will not affect significantly the carrier population but only its spatial distribution. We report here about a device numerical simulation that allows us to analyse the influence of the "i′-layer" position, thickness and density of states on the a-Si: H solar cells performances. Results of some systematic simulation from the ASCA program (Amorphous Solar Cell Analysis), and for different configurations will be presented. © 1994 Materials Research Society.

n/a

n/a

n/a

n/a

n/a

n/a

n/a

n/a

n/a