Process and apparatus for growing a crystal ribbon

A process and apparatus is disclosed for growing a crystal ribbon of a substance of theoretically infinite length from a melt of the substance. A pair of fixedly positioned edge defining members are partially submerged into the melt so as to break the surface of the melt at a predetermined distance from one another. The edge defining members are wettable by the melt and the predetermined distance substantially corresponds to the width of the crystal ribbon to be grown. The crystal ribbon is grown by contacting the surface of the melt with a seed ribbon between the edge defining members whereby a meniscus of the melt is established on the seed ribbon. The meniscus is stabilized by the meniscus of the melt on the edge defining members. Pulling the seed crystal ribbon away from the melt results in continuous growth of the crystal ribbon

Development of improved wraparound contacts for silicon

A developmental process for fabricating 2 X 4 cm back surface field silicon solar cells featuring wraparound contacts and screen printed dielectric isolation is described. The process was then used to fabricate a number of cells for evaluation and study, as well as to establish the validity of the process sequence. While a number of cells exhibiting relatively good conversion efficiencies were produced, nearly all had low I-V curve factors for the level of efficiencies attained. Cells with conversion efficiencies of more than 15 percent (air mass zero and 25 C) had fill factors of only 0.76. Evidence as to the cause of this has not been conclusive, but is most probably linked to isolation failure in the wraparound dielectric and associated shunting problems

Demonstration of the feasibility of automated silicon solar cell fabrication

An analysis of estimated costs indicate that for an annual output of 4,747,000 hexagonal cells (38 mm. on a side) a total factory cost of $0.866 per cell could be achieved. For cells with 14$1.22 per watt of electrical output. A laboratory model of such a facility was operated to produce a series of demonstration runs, producing hexagonal cells, 2 x 2 cm cells and 2 x 4 cm cells

Coplanar back contacts for thin silicon solar cells

A process for fabricating 2 to 3 mil wraparound solar cells was formulated. Sample thin wraparound cells were fabricated using this process. The process used a reinforced perimeter construction to reduce the breakage that occurs during handling of the wafers. A retracting piston post was designed and fabricated to help minimize the breakage that occurs during the screen printing process. Two alternative methods of applying the aluminum back surface field were investigated. In addition to the standard screen printed back surface field, both spin-on and evaporated aluminum techniques were researched. Neither spin-on nor evaporated aluminum made any noticeable improvement over the screen printing technique. A fine screen mesh was chosen for the application of the aluminum paste back surface field. The optimum time and temperature for firing the aluminum turned out to be thirty seconds at 850 C. The development work on the dielectric included looking at three dielectrics for the wraparound application. Transene 1000, Thick Film Systems 1126RCB and an in house formulation 61-2-2A were all tested. Cells with pre-dielectric thickness of 3.0-0-3.5 mils using Transene 1000 as the wraparound dielectric and the procedure outlined above showed an average efficiency of 10.7 percent. Thinner cells were fabricated, but had an unacceptable yield and efficiency

Screen printing technology applied to silicon solar cell fabrication

The process for producing space qualified solar cells in both the conventional and wraparound configuration using screen printing techniques was investigated. Process modifications were chosen that could be easily automated or mechanized. Work was accomplished to optimize the tradeoffs associated with gridline spacing, gridline definition and junction depth. An extensive search for possible front contact metallization was completed. The back surface field structures along with the screen printed back contacts were optimized to produce open circuit voltages of at least an average of 600 millivolts. After all intended modifications on the process sequence were accomplished, the cells were exhaustively tested. Electrical tests at AMO and 28 C were made before and after boiling water immersion, thermal shock, and storage under conditions of high temperature and high humidity

Wildland inventory and resource modeling for Douglas and Carson City Counties, Nevada, using LANDSAT and digital terrain data

The potential of using LANDSAT satellite imagery to map and inventory pinyon-juniper desert forest types in Douglas and Carson City Counties, Nevada was demonstrated. Specific map and statistical products produced include land cover, mechanical operations capability, big game winter range habitat, fire hazard, and forest harvestability. The Nevada Division of Forestry determined that LANDSAT can produce a reliable and low-cost resource data. Added benefits become apparent when the data are linked to a geographical information system (GIS) containing existing ownership, planning, elevation, slope, and aspect information

Mutant Weeds of Iowa: V. S-triazine Resistant Setaria faberi Herrm

S-triazine resistance in giant foxtail (Setaria faberi Herrm.) has been reported previously, but not in the midwestern U.S. corn belt or Iowa. A study was conducted using a chlorophyll fluorescence assay to confirm the presence of resistance in one S. faberi population in Iowa. Variable chlorophyll fluorescence assays confirmed that a population of this species with this type of resistance exists in Iowa. This is the first report of s-triazine resistance in S. faberi, and the fourth species with this type of herbicide resistance, found in an Iowa agroecosystem

Disability in young people and adults one year after head injury: prospective cohort study

OBJECTIVE: To determine the frequency of disability in young people and adults admitted to hospital with a head injury and to estimate the annual incidence in the community. DESIGN: Prospective, hospital based cohort study, with one year follow up of sample stratified by coma score. SETTING: Five acute hospitals in Glasgow. SUBJECTS: 2962 patients (aged 14 years or more) with head injury; 549 (71%) of the 769 patients selected for follow up participated. MAIN OUTCOME MEASURES: Glasgow outcome scale and problem orientated questionnaire. RESULTS: Survival with moderate or severe disability was common after mild head injury (47%, 95% confidence interval 42% to 52%) and similar to that after moderate (45%, 35% to 56%) or severe injury (48%, 36% to 60%). By extrapolation from the population identified (90% of whom had mild injuries), it was estimated that annually in Glasgow (population 909 498) 1400 young people and adults are still disabled one year after head injury. CONCLUSION: The incidence of disability in young people and adults admitted with a head injury is higher than expected. This reflects the high rate of sequelae previously unrecognised in the large number of patients admitted to hospital with an apparently mild head injury

Automated fabrication of back surface field silicon solar cells with screen printed wraparound contacts

The development of a process for fabricating 2 x 4 cm back surface field silicon solar cells having screen printed wraparound contacts is described. This process was specifically designed to be amenable for incorporation into the automated nonvacuum production line. Techniques were developed to permit the use of screen printing for producing improved back surface field structures, wraparound dielectric layers, and wraparound contacts. The optimized process sequence was then used to produce 1852 finished cells. Tests indicated an average conversion efficiency of 11% at AMO and 28 C, with an average degradation of maximum power output of 1.5% after boiling water immersion or thermal shock cycling. Contact adherence was satisfactory after these tests, as well as long term storage at high temperature and high humidity