A New Method of Metallization for Silicon Solar Cells

A low cost ohmic contact on silicon solar cells based on molybdenum-tin metal systems was developed. The approach is based on the formulation of a screenable ink composed from molybdenum oxide and tin mixture. The reduction of Mo03 into Mo and the establishment of Mo 03:Sn ratio is studied. Both tasks were done in an experimental station constructed for this purpose. The results show that molybdenum was formed from its oxide at 800 C. and improved in bonding to silicon at 900 C. A 20% Mo03-80%Sn mixture was converted into metallic coating within this temperature range

Investigation of nickel-silicon metallization process

The metallization of silicon solar cells passivated with silicon nitride coating was investigated by using commercial Ni pastes #5517 from Thick Film Systems, #7028-5 from Cermalloy, experimental formulation # X-A by Sollos, Inc. and evaporated Ti-Ni film. Comparative and reference tests were done with the Dupont Ag paste #7095 and with a mixture of Ni paste #5517 with Ag paste #7095 in the respective ratio of 9 to 1 by weight. The evaluation criteria for the metallization was the mechanical bond strength of the contact, solderability, copper plating ability and electrical characteristics in terms of Voc, Isc values and shape of the V-I curve. The results revealed that the Dupont Ag paste #7095 mt all required criteria, while the quality of the cells metalized with the commercial Ni paste #5517 from Thick Film Systems, #7028-5 from Cermalloy as well as the experimental paste # X-A from Sollos, Inc. was below the acceptable standards. A significant improvement was obtained with the mixture of Ni paste #5517 from Thick Film Systems with 10% addition of Dupont paste # 7095

High reliability bond program using small diameter aluminum wire

The program was undertaken to characterize the performance of small diameter aluminum wire ultrasonically bonded to conductors commonly encountered in hybrid assemblies, and to recommend guidelines for improving this performance. Wire, 25.4, 38.1 and 50.8 um (1, 1.5 and 2 mil), was used with bonding metallization consisting of thick film gold, thin film gold and aluminum as well as conventional aluminum pads on semiconductor chips. The chief tool for evaluating the performance was the double bond pull test in conjunction with a 72 hour - 150 C heat soak and -65 C to +150 C thermal cycling. In practice the thermal cycling was found to have relatively little effect compared to the heat soak. Pull strength will decrease after heat soak as a result of annealing of the aluminum wire; when bonded to thick film gold, the pull strength decreased by about 50% (weakening of the bond interface was the major cause of the reduction). Bonds to thin film gold lost about 30 - 40% of their initial pull strenth; weakening of the wire itself at the bond heel was the predominant cause. Bonds to aluminum substrate metallization lost only about 22%. Bonds between thick and thin film gold substrate metallization and semiconductor chips substantiated the previous conclusions but also showed that in about 20 to 25% of the cases, bond interface failure occurred at the semiconductor chip

Heat addition to a subsonic boundary layer: A preliminary analytical study

A preliminary analytical study of the effects of heat addition to the subsonic boundary layer flow over a typical airfoil shape is presented. This phenomenon becomes of interest in the space shuttle mission since heat absorbed by the wing structure during re-entry will be rejected to the boundary layer during the subsequent low speed maneuvering and landing phase. A survey of existing literature and analytical solutions for both laminar and turbulent flow indicate that a heated surface generally destabilizes the boundary layer. Specifically, the boundary layer thickness is increased, the skin friction at the surface is decreased and the point of flow separation is moved forward. In addition, limited analytical results predict that the angle of attack at which a heated airfoil will stall is significantly less than the stall angle of an unheated wing. These effects could adversely affect the lift and drag, and thus the maneuvering capabilities of booster and orbiter shuttle vehicles

A new method of metallization for silicon solar cells

The new metallization process based on Mo-Sn system was studied. The reaction mechanism of MoO3 and its mixture with Sn was examined. The basic ink composition was modified in order to obtain a low ohmic contact to the cell. The electrical characteristics of the cells were comparable with the existing metallization processes. However, in comparison with the standard processes using silver as the contacting metal, the saving obtained by the use of the new process was substantial

Critical soft landing technology issues for future US space missions

A programmatic need for research and development to support parachute-based landing systems has not existed since the end of the Apollo missions in the mid-1970s. Now, a number of planned space programs require advanced landing capabilities for which the experience and technology base does not currently exist. New requirements for landing on land with controllable, gliding decelerators and for more effective impact attenuation devices justify a renewal of the landing technology development effort that existed during the Mercury, Gemini, and Apollo programs. A study was performed to evaluate the current and projected national capability in landing systems and to identify critical deficiencies in the technology base required to support the Assured Crew Return Vehicle and the Two-Way Manned Transportation System. A technology development program covering eight landing system performance issues is recommended

A theoretical study of non-adiabatic surface effects for a model in the NTF cryogenic wind tunnel

A theoretical analysis was made of the severity and effect of nonadiabatic surface conditions for a model in the NTF cryogenic wind tunnel. The nonadiabatic condition arises from heaters that are used to maintain a constant thermal environment for instrumentation internal to the model. The analysis was made for several axi-symmetric representations of a fuselage cavity, using a finite element heat conduction code. Potential flow and boundary layer codes were used to calculate the convection condition for the exterior surface of the model. The results of the steady state analysis show that it is possible to maintain the surface temperature very near the adiabatic value, with the judicious use of insulating material. Even for the most severe nonadiabatic condition studied, the effects on skin friction drag and displacement thickness were only marginally significant. The thermal analysis also provided an estimate of the power required to maintain a specified cavity temperature

Birds of Golden Pride Project area, Nzega District, central Tanzania: an evaluation of recolonization of rehabilitated areas

In Tanzania, the success of habitat restoration in mining areas to create suitable environmental conditions for wildlife is poorly understood. Between March 2010 and December 2014 bird species were recorded at the Golden Pride Project area, a gold mine in Nzega District, central Tanzania. The aims of this study were to document bird communities in the mine area, and to assess the extent to which rehabilitated areas have been recolonised. Mist netting, point counts, timed species counts and opportunistic observations were used to document 181 species of birds at the mine area. These included two species endemic to Tanzania, the Tanzanian Red-billed Hornbill Tockus ruahae (treated here as a species separate from T. erythrorhynchus, see Kemp & Delport 2002, Sinclair & Ryan 2010) and Ashy Starling Cosmopsarus unicolor. Rehabilitated areas had about half the number of species found in the unmined areas. Bird use of areas under rehabilitation suggests that habitat restoration can be used to create corridors linking fragmented landscapes. Results suggest that as the vegetation of the rehabilitated areas becomes more structurally complex, the number of bird species found there will be similar to those in unmined areas. This study provides a baseline for future monitoring, leading to a better understanding of the process of avian colonisation of rehabilitated areas. Furthermore, results imply that in mining areas it is useful to have an unmined area where vegetation is naturally allowed to regenerate, free of human activity. These unmined areas can later act as source habitats from which birds can disperse into rehabilitation areas once the vegetation structure is sufficiently complex