Moisture ingress prediction in polyisobutylene‐based edge seal with molecular sieve desiccant

Abstract

Often photovoltaic modules are constructed with materials that are sensitive to water. This is most often the case with thin film technologies, including perovskite cells, where the active layers are a few microns thick and can be sensitive to moisture, liquid water or both. When moisture or liquid water can ingress, a small amount of water can lead to corrosion and depending on the resulting reactions, a larger local detrimental effect is possible. To prevent moisture from contacting photovoltaic components, impermeable frontsheets and backsheets are used with a polyisobutylene (PIB)‐based edge seal material around the perimeter. Here, we evaluate the ability of a PIB‐based edge seal using a molecular sieve desiccant to keep moisture out for the expected module lifetime. Moisture ingress is evaluated using test coupons where the edge seal is placed between 2 pieces of glass, one of which has a metallic calcium film on it, and monitoring the moisture ingress distance as a function of time. We expose samples to different temperature and humidity conditions to create permeation models useful for extrapolation to field use. This extrapolation indicates that this PIB material is capable of keeping moisture out of a module for the desired lifetime.

Package Development for Reliability Testing of Perovskites

“…A properly constructed edge seal should enable decades of outdoor testing. To enable 25 years of outdoor use requires only 0.41 cm in Denver, Colorado, compared to 1.1 cm in Bangkok, Thailand, based on typical meteorological year data for those regions. , In a set location, since the edge seal is slowing a diffusion process, a doubling of edge seal width should increase the breakthrough time by a factor of 4. By dedicating a minimum amount of package real estate to the edge seal, using impermeable glass front and back sheets and a low thermal budget to minimize changes to the device enables researchers to decouple their studies of the intrinsic stability of their devices from package failure.…”

“…It should also be possible to deconstruct a package for post-mortem analysis with careful, patient use of a razor blade. If smaller packaged samples are desired due to space constraints (e.g., under continuous illumination in a degradation setup), the edge seal requirements can be readily calculated for a particular temperature/​humidity/​time requirement . Those who might choose to reduce the edge seal width are encouraged to still build in some safety factor in the event of imperfectly constructed seals due to poor sample cleaning/​assembly/​bubble formation/​user variability.…”

“…For outdoor tests, a piece of polyethylene terephthalate (PET) coated with calcium metal was encased in the package to indicate the package integrity. Ca metal is very sensitive to air and moisture, and upon exposure, it will convert to Ca­(OH) 2 and turn transparent . After 13.5 months, all packages remained hermetically sealed (Figure S2).…”

“…If smaller packaged samples are desired due to space constraints (e.g., under continuous illumination in a degradation setup), the edge seal requirements can be readily calculated for a particular temperature/ humidity/time requirement. 13 Those who might choose to reduce the edge seal width are encouraged to still build in some safety factor in the event of imperfectly constructed seals due to poor sample cleaning/assembly/bubble formation/user variability. If a reduced seal width is acceptable, one may consider a "hybrid" flip-chip package where a reduced edge seal is used directly between the cell coupon and metal feed through substrate to eliminate the glass coverslip.…”

“…Ca metal is very sensitive to air and moisture, and upon exposure, it will convert to Ca(OH) 2 and turn transparent. 13 After 13.5 months, all packages remained hermetically sealed (Figure S2). However, the PIB pressed with the lowest hot plate temperature of 100 °C initially contained many bubbles.…”