Damp heat resilient thermoplastic polyolefin encapsulant for photovoltaic module encapsulation

Abstract

Thermoplastic polyolefin (TPO) is a non-crosslinking material used in photovoltaic module encapsulation. TPO thermal degradation and its weather stabilities are still not known. In this work, TPO laminates were prepared and subjected to extended damp-heat weather test. TPO encapsulant properties were studied and compared with the most commonly used encapsulant, Ethylene-Vinyl Acetate (EVA). Four times lower rate of transmittance loss and increment rate in the yellowness index values have been found for TPO compared to EVA laminate. Damp-heat induced degradation mechanism, and its components were studied using Raman and Fourier-transform-infrared (FTIR) spectroscopy. Raman spectra revealed that the carbonyl group loss rate at the edge is one order of magnitude higher than the center. FTIR has shown a higher rate of acetic acid and hydroxyl group formation in EVA as compared to the TPO. FTIR also demonstrated that TPO has a lower water absorption because of its nonpolar nature, whereas EVA shows more water absorption due to its polar nature. The rate of change in thermal properties of TPO and EVA encapsulants were studied through the heat-cool-heat cycle. A higher rate of increment in the degree of crystallinity is found for EVA as compared to the TPO encapsulant during the extended damp-heat acceleration test. This study helps to understand the TPO and EVA encapsulants degradation behavior, degradation components, and mechanism to the encapsulant researchers and PV module manufacturers when a PV module experiences the hot-humid conditions. This TPO may result in the industry adopting the different PV modules for fabricating.