Advanced Manufacturing Laboratory    



Renewable Energy: Laser Assisted Processing of Composite Materials and Solar Cells


Inter-Laminar Toughening of Composites for Wind Turbine Blade Application

A novel process is proposed for the inter-laminar toughening of continuous fiber reinforced polymer matrix composites (PMCs).  A strong interest exists in enhancing the toughness of large, tapered laminate composites such as wind turbine blades fabricated from vacuum assisted resin transfer molding (VARTM).  The need to toughen PMCs arises from the matrix dominated fracture properties between laminae, resulting in preferential planar fiber/matrix de-bonding (delamination).  The proposed process selectively bonds fiber reinforcement fabrics with a tough thermoplastic (TP) interleaf prior to VARTM.  The method is particularly beneficial for stress concentration locations such as ply terminations (drop-offs), free edges, and holes.

To develop a process to form tough interleaves in a laminate PMC without disrupting the fiber architecture or degrading its in-plane strength, thorough understanding of heat transfer, chemical adhesion, polymer inter-diffusion, and bonding between the interleaf, the fiber reinforcement, and matrix materials is vital.  This process presents significant challenges requiring the development of predictive capabilities for interleaf morphology and quality through the modeling of localized thermal and chemical reactions.  To fully understand the effects of reinforcement quality on the delamination behavior of laminate PMCs, rigorous mechanical testing and characterization is required.

Selective interleaving of preform laminate composites will be accomplished through hot melt bonding of select polymers to dry fibers prior to VARTM fabrication.  The selection and characterization of the interleaf material is critical to enhance fiber and matrix bonding during the hot melt and curing processes.  A ductile TP with a low glass transition temperature (amorphous) and chemically compatible to epoxy (containing bisphenol-A) is desired to maximize bonding.  Characterization methods including cross sectioning with optical microscopy and computed tomography will be applied to study the effects of heating parameters on the interleaf morphology and structure.   The delamination resistance, in both static and fatigue loading conditions will be tested. 



Glass-Side Laser Scribing of Multilayer Thin Film Solar Cells

Laser scribing is an important manufacturing process used to reduce photocurrent and resistance losses and increase solar cell efficiency through the formation of serial interconnections in large-area thin-film solar cells. In recent years, the use of glass-side laser scribing processes has led to increased scribe quality and solar cell efficiencies, however, defects introduced during the process such as thermal effect, micro cracks, film delamination, and removal uncleanliness keep the modules from reaching their theoretical efficiencies.

Since glass-side laser scribing is applicable to most thin-film solar panel manufacturing, such as CdTe, a-Si:H and CIGS. This project uses CdTe solar cell as an example, to experimentally and numerically investigate the effect of laser processing conditions on defect formation, understand how to reduce these defects, and establish reliable prediction capabilities. Also, a defect mitigation strategy will be developed based on the analysis of the changes in solar cell electrical properties, such as contact resistances, current output and efficiencies, and their connections with the defects.