R2R fabrication of multiply indented, hybrid 3D-nanobowls with ultra-high haze for efficiently light trapping

Light trapping by nanostructures featuring high transmittance and high haze represents a viable strategy to boost solar cell efficiency via enhanced light absorption. However, low-cost, large-area, and eco-friendly fabrication approaches for such light trapping structures remain elusive. Herein, we demonstrate a new design of film with multiply indented, hybrid three-dimensional (3D)-nanobowls, which can reduce light reflection at large angles by together enhancing light scattering, transmittance, and haze. This kind of nanostructures is generated via roll-to-roll (R2R) UV-nanoimprint process, where the critical template is fabricated by taking advantage of metal displacement reaction between aluminum and zinc ions. The as-fabricated light-trapping film shows ultra-high haze of 98% while keeping favorable transmittance of 87%. Therefore, this light-trapping film, adhered onto polysilicon solar cells, enhances the short-circuit current (J_SC) from 4.26% at solar illumination angle of 0°, up to 65.95% at large angle of 85°, as well as 14.29% onto organic solar cells (OSC) under indoor light. To validate practical feasibility, day-time (13-hour) outdoor large-format polysilicon cells experiments reveal that the J_SC was enhanced by 5.68% under the sunny condition and 13.6% under the cloudy condition. Furthermore, this film exhibits self-cleaning performance with a water contact angle (WCA) of up to 140°. More importantly, this kind of high-performance film can be fabricated up to more than 25 m within 1 min using our R2R process, demonstrating the high throughput and low cost capability, well meeting the demand for solar cell industry.