Correlation study of damp heat and pressure cooker testing on backsheets

Abstract

For photovoltaic (PV) modules, high‐quality backsheets are essential. To verify these qualities, hot and humid tests of up to 1000 h are standard in the PV industry. Damp heat (DH) tests are useful for evaluating material quality and infant failures, especially for materials that are sensitive to hydrolysis. However, shorter test periods are needed. Hence, the objective of this study was to investigate and correlate the aging behavior of hydrolysis‐sensitive polyester [poly(ethylene terephthalate) (PET)] based backsheets after exposure to DH and pressure cooker conditions. The material properties, such as thermal and mechanical parameters, correlated well between the pressure cooker at 120 °C and the DH test, with the qualification that differences in the failure mechanism were seen after 96 and 2000 h, respectively. Nevertheless, it should be acceptable to use pressure cooker tests (PCTs) for fast material testing. The PCT is proposed to significantly reduce the testing time for infant failures and material quality to around 4 days for PET‐based backsheets. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44230.

A novel test method for quantifying cracking propensity of photovoltaic backsheets after ultraviolet exposure

“…Without UV irradiation, there is no significant change observed in either surface morphology or ATR‐FTIR spectrum (c.f. dashed lines in Figure C, D), which is consistent with the results reported in literature …”

“…It is worthwhile to note that the samples aged in UV humid conditions for 700 hours randomly presented an early sign of delamination during the tensile testing. The increase of elastic moduli after aging (Figure C) was probably because of the combination of physical annealing, chemical aging, and chemocrystallization at elevated temperature . The competition between recrystallization and PET degradation depends on the stress level of aging condition and time.…”

“…dashed lines in Figure 6C, D), which is consistent with the results reported in literature. 12 The above chemical and morphologic results have indicated that the surface degradation of the PPE is highly dependent on environmental conditions, and UV irradiation is one of main factors. The surface embrittlement caused by this degradation substantially reduced the fracture energy of the UV-exposed backsheets (…”

“…Extensive efforts have been made to characterize the backsheet degradation based on changes in yellowing, chemical structure and microstructure, tensile strength, adhesion strength, and other bulk thermo or mechanical properties . However, limited studies have investigated backsheet cracking, probably because it is challenging to reproduce the cracking observed in the field using accelerated aging tests.…”

“…6,7 The cracking has been postulated to be the result of embrittlement of the surface layer caused by prolonged ultraviolet (UV) exposure even though these polymeric materials are UV-stabilized and/or pigmented. [8][9][10] Extensive efforts have been made to characterize the backsheet degradation based on changes in yellowing, 5,11 chemical structure and microstructure, 4,5,11,12 tensile strength, 2,5,[12][13][14] adhesion strength, 2,3,15,16 and other bulk thermo or mechanical properties. 17,18 However, limited studies have investigated backsheet cracking, 5,19 probably because it is challenging to reproduce the cracking observed in the field using accelerated aging tests.…”