The Effect of Laminate Construction and Temperature Cycling on the Fracture Strength and Performance of Encapsulated Solar Cells

A critical aspect of silicon solar module reliability is the fracture characteristics of the solar cells under mechanical loads. Here, we use 3-point bend testing of coupons to investigate the effects of tabbing, encapsulant and thermal history on the fracture strength of silicon solar cells. We find that the fracture strength depends significantly on the encapsulant modulus and thickness. Doubling the encapsulant thickness can increase the load at fracture by 80%. In addition, short exposure to low temperatures (<; -20C) can decrease the room temperature fracture strength by 80% or more. The mechanism of this effect is described as contraction of the encapsulant thickness adjacent to the ribbon which bends the cell sharply over the ribbon. This low temperature effect on crack susceptibility is not currently captured in standard durability testing sequences. Finally, the amount of crack damage depends on the strain at fracture and the power loss can be as high as 30%. Degradation behavior in extended temperature cycling of fractured cells also depends on the initial fracture pattern.