Thermomechanical damages in the vicinity of wires in photovoltaics assemblies exposed to large amplitude thermal cycling

Abstract

The advent of low Earth orbit constellations triggers a renewed interest in silicon-based space photovoltaic assemblies (PVA). However, given the harsh operational conditions in orbit, terrestrial silicon technologies need adaptations to gain reliability in space environments. This work focuses on the effects of -120 $°C$/+120 $°C$ atmospheric pressure thermal cycling (APTC) on wire-interconnected Si PVA. Glass-glass laminates with varying adhesive thicknesses were manufactured, and their APTC failure modes analyzed. This experimental work demonstrated that glass cracks above wires and cell cracks under wires appear with thin adhesive layers, while PVA with a thicker adhesive did not experience such failures. To gain insight into the thermomechanics in the vicinity of interconnection wires during thermal cycling, an analytical and a finite element models were developed. In good agreement with experimental observations, it was found that reducing the adhesive thickness reduces damages in the cell and glass. Furthermore, to keep PVA lightweight, the analytical model shows that wire diameter reduction allows similar stress mitigation. Other paths are also discussed, such as glass thickness and adhesive shear modulus reductions along with improved wires alignments. Finally, comparable issues can occur in standard terrestrial modules; the problem being quite generic, model and design rules reported here are believed to be relevant to tackle them as well.