Roll‐to‐Roll <scp>UV</scp> Embossing and Pressure Thermoforming of <scp>PET</scp> Films for Spherical Fresnel Lenses in Photovoltaic Applications

ABSTRACT Integrating Fresnel lenses into photovoltaic (PV) systems can reduce the required solar‐cell area and enhance conversion efficiency by concentrating incident sunlight onto the cell surface. In this study, planar and spherical Fresnel lenses were designed and optimized through optical simulations to develop high‐concentration lenses for PV applications. The simulations indicated that a spherical Fresnel lens with a curvature radius of 250 mm provided the highest illumination. However, conventional mass production of spherical Fresnel lenses remains cost‐prohibitive due to the complexity and expense of machining spherical molds. To overcome this limitation, we propose an innovative and cost‐effective fabrication method that reduces mold manufacturing costs and simplifies the production workflow. The process employs roll‐to‐roll UV embossing as the initial patterning step, followed by pressure‐assisted thermoforming to reshape the patterned film into a spherical form. The Taguchi method was used to optimize key process parameters, including resin temperature, film speed, film‐press pressure, and film tension. Among these, film tension had the most significant effect on the structural fidelity of the Fresnel features. In the thermoforming stage, six groups of spherical Fresnel lenses were produced under varying conditions, and their PV performance was evaluated using a solar simulator. The results showed that the PV conversion efficiency increased from 8.88% (bare solar cell) to 56.73% when using the planar Fresnel lens, corresponding to 6.39× the bare‐cell value. Furthermore, the spherical Fresnel lens provided an additional 23% improvement over the planar lens. These results demonstrate that the proposed hybrid process enables the fabrication of functional polymer‐based Fresnel lenses and effectively enhances PV performance.