Investigation of the effects of sub-threshold high energy electrons on the properties of silicon photovoltaic cells Final report, 3 Feb. - 3 Nov. 1969

Photovoltaic characteristics of p-n and n-p Si cells and p-n lithium-doped cells irradiated with high energy electron

Summary of theoretical and experimental investigation of grating type, silicon photovoltaic cells

Theoretical and experimental aspects are summarized for single crystal, silicon photovoltaic devices made by forming a grating pattern of p/n junctions on the light receiving surface of the base crystal. Based on the general semiconductor equations, a mathematical description is presented for the photovoltaic properties of such grating-like structures in a two dimensional form. The resulting second order elliptical equation is solved by computer modeling to give solutions for various, reasonable, initial values of bulk resistivity, excess carrier concentration, and surface recombination velocity. The validity of the computer model is established by comparison with p/n devices produced by alloying an aluminum grating pattern into the surface of n-type silicon wafers. Current voltage characteristics and spectral response curves are presented for cells of this type constructed on wafers of different resistivities and orientations

Investigation of the effects of sub-threshold high energy electrons on the properties of silicon photovoltaic cells Midway report, 3 Feb. - 3 Aug. 1969

Subthreshold electron irradiation effects on semiconductor surface

Efficiency of tandem solar cell systems as function of temperature and solar energy concentration ratio

The results of a comprehensive theoretical analysis of tandem photovoltaic solar cells as a function of temperature and solar concentration ratio are presented. The overall efficiencies of tandem cell stacks consisting of as many as 24 cells having gaps in the 0.7 to 3.6 eV range were calculated for temperatures of 200, 300, 400, and 500 K and for illumination by an AMO solar spectrum having concentration ratios of 1, 100, 500, and 1000 suns. For ideal diodes (A = B = 1), the calculations show that the optimized overall efficiency has a limiting value eta sub opt of approximately 70 percent for T = 200 K and C = 1000; for T = 300 K and C = 1000, this limiting efficiency approaches 60 percent

Photovoltaic Effect and Utilization of Cells Semiannual Report, Jul. 1 - Dec. 31, 1966

Effects of electron irradiation on surface recombination velocity of n and p type silicon photovoltaic cells of various resistivitie

Capacitance transients in p-type GaAs MOS structures and application to lifetime mapping during solar cell fabrication

Fabrication on p-type GaAs of MOS structures in which the quality of the oxide is such that the surface can be driven into deep inversion by a voltage pulse is reported. The capacitance transients in such MOS capacitors as a function of step amplitude and temperature were measured and the transients were analyzed by an extension of a method for silicon. The oxides were produced by plasma oxidation on an LPE-grown p-type GaAs specimen with N sub A of 3x10 to the 17th power/cu cm. The capacitors were produced by depositing 50 microns-diameter gold dots over the native oxide and, therefore, the lifetime is localized to the area under the dot. The method permits extraction of both the bulk lifetime and the interface recombination velocity. These parameters on samples with different N sub A were measured and a correlation between tau sub g and N sub A was found

Deposition and characterization of ZnS/Si heterojunctions produced by vacuum evaporation

Isotype heterojunctions of ZnS (lattice constant 5.41 A) were grown on silicon (lattice constant 5.43 A) p-n junctions to form a minority-carrier mirror. The deposition process was vacuum evaporation from a ZnS powder source onto a heated (450 C) substrate. Both planar (100) and textured (111) surfaces were used. A reduction of the minority-carrier recombination at the surface was seen from increased short-wavelength quantum response and increased illuminated open-circuit voltage. The minority-carrier diffusion length was not degraded by the process

Creep Modeling of Wood Using Time-Temperature Superposition

The time-temperature superposition principle was used to develop long-term compression creep and recovery models for southern pine exposed to constant environmental conditions using shortterm data. Creep (17-hour) and recovery (40-hour) data were obtained at constant temperature levels ranging from 70 F to 150 F and constant equilibrium moisture content (EMC) of 9%. The data were plotted against log-time, and the resultant curve segments were shifted along the log-time axis with respect to the curve for ambient conditions to construct a master curve applicable to ambient conditions (70 F, 9% EMC) and a longer time period. The master curves were represented by power functions, and they predicted up to 6.4 years of creep and 5.8 years of recovery response. The validity of the master curves for predicting creep of wood exposed to the normal interior environment in buildings was tested by conducting ten-month creep tests in the laboratory. The fluctuating environment caused geometry changes in the surface of the specimens affecting the collected long-term data. Therefore, a good comparison between the master curves and the long-term data was not possible

Image Correlation Analysis of Multiple-Bolt Wood Connections

Displacement beneath the bolts in multiple-bolted wood connections was studied using digital image correlation. This method combines digital image analysis and image correlation to calculate surface displacements from a set of digitized video images of an object under an applied load. Double-shear connections constructed of clear, straight-grained yellow-popular were tested in compression parallel to grain. Five different bolt patterns were used to analyze the effect of number of bolts in a vertical row and number of bolts in a horizontal column on displacement distribution among bolts. It was discovered that for multi-bolt patterns in a vertical row, parallel to load displacements below the outer bolts, are higher than those below the center bolt(s) but not equal in magnitude as previously assumed and the surface displacements perpendicular to the load beneath the bolts split along the centerline of the bolts. Variation in material properties, rigid body motion, eccentric loading and/or wood failure beneath a bolt are detectable with digital image correlation and may influence the results if not carefully considered in experimental design

Analysis of Racked Wood Pallets

A rational analysis procedure for designing wood stringer pallets for use in warehouse storage racks was developed for manufacturers and pallet users and is part of a computerized automatic design and analysis program called the Pallet Design System (PDS). The procedure uses simplified analog models of pallets and matrix structural analysis methods to compute the stress and deflection of critical structural elements. Semi-rigid nail joints are modeled as spring elements. Pallets with 2, 3, 4, or 5 stringers and up to 15 deckboards can be analyzed with a variety of load types including distributed and concentrated loads. The strength and stiffness of experimental pallets were compared to predicted values and showed good agreement