A High-Performance CO2-Based Polycarbonate-Type Polyurethane toward Reliable Photovoltaic Encapsulation

Abstract

Photovoltaic (PV) encapsulants play a pivotal role in ensuring the long-term reliability of solar modules by protecting sensitive cells from moisture ingress, mechanical stress, and ultraviolet (UV) degradation. However, conventional encapsulant materials, such as ethylene-vinyl acetate, polyolefin elastomer, and polyvinyl butyral, exhibit several inherent limitations, including a high water vapor transmission rate, poor delamination resistance, and easy formation of optical haze under long-term UV irradiation in hygrothermal conditions. To address these challenges, we herein design a CO2-derived aliphatic polycarbonate-based thermoplastic polyurethane (TPU) as a PV encapsulant, which combines high transmittance (>90.5%), flexibility, superior water vapor barrier properties (WVP < 12.42 g·mm m–2 day–1), moisture insensitivity, and strong adhesion to PV glass and backsheet substrates. More specifically, the multiblock TPU is synthesized via the polyaddition of poly(propylene carbonate)diol, polyether diol, hexamethylene diisocyanate, and 1,4-butanediol. Upon optimizing the chemical composition and incorporating proper additives (e.g., silicone coupling agents, UV absorbers, antioxidants), the encapsulant achieves enhanced interfacial adhesion with a peel strength of 87.2 N cm–1 and maintains a residual peel strength of 73.4 N cm–1 following accelerated UV aging. Additionally, the adhesion mechanism based on TPU is proposed and preliminarily elucidated. This study tackles key challenges in photovoltaic module encapsulation by developing this high-performance alternative material, demonstrating significant potential for large-scale industrial applications.