Marty W. Degroot

Barrier technology providing exceptional stability of CIGS devices under accelerated damp heat conditions

Parallel to rapid prototype testing for moisture barrier performance, extensive failure mode analyses of inorganic direct cell coatings for CIGS solar cells have led to important conclusions regarding barrier degradation during exposure. Based on these analyses, a new strategy for direct cell barrier film technology has been developed that eliminates the primary root causes of failure. This approach provides exceptional damp heat stability to CIGS devices, even in the absence of additional encapsulation technology. Evaluation of time-to-failure data resulted in characteristic lifetime estimates of >1500 h at 85°C/85% RH for the new barrier film approach, compared to ∼500 h for various silicon nitride based films under the same conditions. In fact, laboratory scale CIGS devices with the improved direct cell coating show >70% probability of surpassing 1000 h under damp heat stress and several cells have survived >3000 h under these conditions with less than 10% reduction in efficiency.

High throughput methodology for evaluation of the moisture barrier performance of thin films for PV applications

We describe a high throughput methodology for evaluation of moisture barrier performance of thin films based on the change in optical density of Al/glass substrates during exposure to high temperature/humidity conditions. This approach has enabled a comparative analysis of hundreds of single and multilayer barrier films and has provided predictive models to identify key input variables that affect moisture barrier performance as well as candidates for protection of thin film solar cells. The data is also utilized to identify different degradation modes that can be correlated with film attributes. The methodology has proved to be valuable in other aspects of thin film lifetime studies, such as the evaluation of transparent conductive oxide material properties as window layers in solar cell applications.

CMP material development for ceria-based applications

New polyurethane pad materials have been developed for chemical mechanical planarization using ceria-based slurries. The optimization of material properties, tailored for effective texture generation with current conditioning schemes, has resulted in improvements in both removal rate stability and defectivity versus conventional CMP pads. Further developments in polymer engineering have led to the demonstration of new polyurethane materials exhibiting up to 30% removal rate increase and lower defectivity versus the industry standard pad in ceria applications.

Soft CMP pads for low defectivity in CMP processes

New approaches to soft polyurethane materials have been developed with the characteristics of high texturability and tunability in physical properties. The approach has resulted in low defectivity and high performance stability in a range of sensitive CMP applications, including copper barrier applications.

Assembly processes for thin film CIGS solar cells: Approaches for improving interconnect repeatability and costs

We have developed new assembly equipment for manufacturing interconnected CIGS solar cell strings that delivers improved control of mechanical tolerances and improved form factor flexibility. The assembly approach is based upon the use of pallets that ensure alignment of solar cells and ribbons during the assembly and curing process. An overview of the assembly equipment is provided. Also discussed are the results of an improved multi-wire interconnect technology that provides a 10% reduction in series resistance relative to standard strings with interconnects provided via electrically conductive adhesive.