Strength of Si Wafers with Microcracks: A Theoretical Model; Preprint

This paper concentrates on the modeling of the strength of photovoltaic (PV) wafers. First a multimodal Weibull distribution is presented for the strength of a silicon specimen with bulk, surface, and edge imperfections. Next, a specific case is analyzed of a PV wafer with surface damage that takes the form of subsurface microcracks

Strength of Si Wafers with Microcracks: A Theoretical Model (Poster)

A new analytical expression that takes into account the surface, edge, and bulk properties of a wafer has been proposed to describe the strength of the brittle materials. A new proposed fracture-mechanics numerical simulation successfully predicted the strength of the cast silicon wafers. It has been shown that the predicted wafer strength distribution agrees well with the available experimental results

Dislocation Generation by Thermal Stresses in Si: Modeling and Experiments

We developed a finite-element modeling program to predict the thermally generated dislocation distribution in a wafer. This model uses measured parameters that are determined from generating dislocations under a known optical flux

Analyses of Failure Mechanisms and Residual Stresses in Graphite/Polyimide Composites Subjected to Shear Dominated Biaxial Loads

This research contributes to the understanding of macro- and micro-failure mechanisms in woven fabric polyimide matrix composites based on medium and high modulus graphite fibers tested under biaxial, shear dominated stress conditions over a temperature range of -50 C to 315 C. The goal of this research is also to provide a testing methodology for determining residual stress distributions in unidirectional, cross/ply and fabric graphite/polyimide composites using the concept of embedded metallic inclusions and X-ray diffraction (XRD) measurements

Light-Induced Passivation of Si by Iodine Ethanol Solution: Preprint

We report on our observations of light-activated passivation of silicon surfaces by iodine-ethanol solution

Wafer Preparation and Iodine-Ethanol-Ethanol Passivation Procedure for Reproducible Minority-Carrier Lifetime Measurement: Preprint

This paper describes reasons that lifetime measurments may be irreproducible using iodine-in-ethanol (I-E) passivation. Possible factors include the strength of the iodine in ethanol solution, wafer cleaning procedures, influence of wafer container during lifetime measurement, and stability of I-E

Wafer Preparation and Iodine-Ethanol Passivation Procedure for Reproducible Minority-Carrier Lifetime Measurement (Poster)

Measurement of the bulk minority-carrier lifetime (T{sub b}) by optical methods, such as photocurrent decay or quasi-steady-state photoconductance (QSSPC), is strongly influenced by surface recombination. Several techniques are known to lower the effective surface recombination velocity, including the following: use of oxidation, floating N/P junction, SiN:H layer, HF immersion, and use of iodine in ethanol or methanol (I-E solution). Using I-E appears to be very simple and does not require any high-temperature treatment such as oxidation, diffusion, or nitridation processes, which can change T{sub b}. However, this is not a preferred procedure within the photovoltaic community because it is difficult to obtain same T{sub b} values reproducibly, particularly when the wafer lifetime is long. The objectives are: (1) Investigate various reasons why lifetime measurements may be irreproducible using I-E solution passivation. (2) Study the influence of the strength of iodine in the ethanol solution, wafer-cleaning procedures, influence of the wafer container during lifetime measurements, and the stability of I-E. (3) Compare lifetimes of wafers (having different T{sub b}) by various techniques such as QSSPC and transient photoconductive decay using short laser pulses of different light intensity; (4) Make minority-carrier diffusion length (L) measurements by a surface photovoltage technique, and to use T{sub b} and L data to determine diffusivity (D) values for various impurity and defect concentrations, using the relationship L{sup 2} = D* T{sub b}

Studies on Backside Al-Contact Formation in Si Solar Cells: Fundamental Mechanisms; Preprint

This paper describes our investigations on the formation of back contacts in screen-printed solar cells, and how most requirements of a good back contact can be met by a suitable process