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

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 CO 2 -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.