In this paper the electrochemical and galvanic corrosion properties of thin-film photovoltaic (TF-PV) module and module sub-components are determined and interpreted in light of established corrosion science. Results of a detailed study of thin-film aluminum metallization corrosion are presented. "Bar-graph'' corrosion, observed in fielded modules, has been experimentally induced and determined to be electrochemical in nature. Corrosion rates and passivation techniques for TF-PV modules are discussed.

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This paper reports on mechanisms by which moisture enters photovoltaic modules and on techniques for reducing such interactions. Results from a study of the effectiveness of various module sealants are reported. quantity of moisture ingress are discussed. It is shown that scribe lines and porous frit bridging conductors provide preferential paths for moisture ingress and that moisture diffusion by surface/interfacial paths is a considerably more rapid process than by bulk paths, which implies that thinfilm substrate and superstrate modules are much more vulnerable to moist environments than are bul k-encapsulated crystalline-silicon modules. Design approaches to reduce moisture entry are discussed.

With flexible leaded parts, the solder-joint failure process involves a complex interplay of creep and fatigue mechanisms. To better understand the role of creep in typical multi-hour cyclic loading conditions, a specialized non-linear finite-element creep simulation computer program has been formulated. The numerical algorithm includes the complete part-lead-solder-PWB system, accounting for strain-rate dependence of creep on applied stress and temperature, and the role of the part-lead dimensions and flexibility that determine the total creep deflection (solder strain range) during stress relaxation. The computer program has been used to explore the effects of various solder creep-fatigue parameters such as lead height and stiffness, thermal-cycle test profile, and part/board differential thermal expansion properties. One of the most interesting findings is the strong presence of unidirectional creep-ratcheting that occurs during thermal cycling due to temperature dominated strain-rate effects. To corroborate the solder fatigue model predictions, a number of carefully controlled thermal-cycle tests have been conducted using special bimetallic test boards.

An investigation of interconnect fatigue in photovoltaic systems has led to the development of useful reliability-design and life-prediction algorithms presented here. Experimental data gathered in this study indicate that the classical strain-cycle (fatigue) curve for the interconnect material fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming, a functional form is fitted to experimental cumulative interconnect failure-rate data to yield statistical fatigue curves (with failure probability as a parameter) that enable (a) the prediction of cumulative interconnect failures during the design life of an array field, and (b) the unambiguous—i.e., quantitative—interpretation of data from field-service qualification (accelerated thermal-cycling) tests. Optimal interconnect cost-reliability design algorithms are derived, intended to minimize the cost of energy over the design life of the array field. This procedure yields not only the minimum break-even cost of delivered energy, but also the required degree of interconnect redundancy and an estimate of array power degradation during the design life of the array field. The usefulness of the design algorithms is demonstrated with realistic examples of design optimization, prediction, and service qualification testing.