Robert D. Wieting

Progress in CIS-based module development

Alloys of copper indium diselenide are the most promising candidates for reducing the cost of photovoltaics below the cost of crystalline silicon. Small area, fully integrated modules exceed 13% in efficiency and long-term outdoor stability has been demonstrated. The availability of natural resources and environmental impacts appear acceptable. Challenges remain to scale the process to larger area and to pass accelerated environmental testing. Process scale-up is systematically proceeding from the foundation of a reproducible small area module process with low variation; however, large-area circuit performance has not yet achieved the same level as the baseline process. Differences in performance between the baseline and large area processes have been isolated to differences in the equipment used to form absorbers and is the subject of current development. The impact of larger part size has been tested for each process step using the demonstrated baseline process. Results indicate that larger-area parts w...

A more elemental examination of factors governing PV module environmental stability

Photovoltaic module reliability studies are essential in understanding both the technical and commercial design lives of various photovoltaic modules. The fundamental parameters affecting photovoltaic module stability are typically not measured for baseline analysis. This study examines these questions in context of fundamental parameters, in an attempt to gain insight at a more elemental level than possible using power measurements. One of the fundamental parameters in PV module reliability is the adhesion of the encapsulant EVA to various module surfaces. The analysis of surface adhesion, both in its initial state, and as it changes with various exposures is studied, primarily focusing on adhesion of EVA to glass, cell surfaces and the interconnect ribbon. Of particular interest is the affect of manufacturing processes and surface cleanliness on this bond strength. Siemens Solar Industries, with Springborn Laboratories have begun analyzing adhesion of EVA using a systematic and statistical method of sample coupons measured at multiple points, and through numerous exposures. Specifically, several EVA types were compared for adhesion characteristics. Measurements of EVA adhesion and how it is affected by surface contamination due to residual solder flux have also been specifically quantified. The summary analysis looked at EVA bonds as a function of environmental exposures. The results of this analysis shows that initial strength of EVA bonds are quite high, these are diminished by both surface contamination effects and environmental exposures.