Two-dimensional correlation spectroscopy studies on degradation of photovoltaic backsheets from indoor to outdoor

Abstract

Degradation of photovoltaic (PV) backsheets is a crucial issue to malfunctions of PV system during their long-term field operations. There is a lack of understanding on the degradation mechanisms of PV backsheets under multiple weathering conditions due to the complexity of the types and sequence of formation of different degradation products. To address this problem, we used the two-dimensional (2D) correlation analysis of infrared (IR) spectra to study the degradation of a typical polyethylene terephthalate (PET)-based PV backsheet, PET/PET/ethylene vinyl acetate (EVA) (PPE), by deconvoluting overlapped bands of different degradation species. The PPE backsheets were exposed to ultra-violet (UV) radiation on the NIST (National Institute of Standards and Technology) SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) at two temperatures (45 °C and 85 °C) in dry condition (relative humidity (RH) ≈ 0%) for 40 days. Outdoor weathering was also conducted at three different sites up to 9 months, comprising a variety of climates, including tropical monsoonal, humid subtropical, and hot arid. The 2D correlation analysis explicitly showed that the PPE backsheets aged at 85 °C under UV not only had faster degradation rate but also had different dominant degradation products compared to the PPE aged at 45 °C. Degradation accelerated at lower 45 °C was found closer to that in field conditions investigated in this work. Therefore, when designing accelerated laboratory experiments, it is important to consider climatic-specific aging parameters for building reliable predictive models for degradation of PV materials.