Part of the book: Updates in Advanced Lithography
In this chapter, the fabrication and replication of periodic nanopyramid structures suitable for antireflection and self-cleaning surfaces are presented. Laser interference lithography (LIL), dry etching, wet etching, and UV nanoimprint lithography (UV-NIL) are employed for the fabrication and replication of periodic nanopyramid structures. Inverted nanopyramid structures were fabricated on Si substrates by LIL and subsequent pattern transfer process using reactive ion etching, followed by potassium hydroxide (KOH) wet etching. The fabricated periodic inverted nanopyramid structures were utilized as a master mold for the nanoimprint process. The upright nanopyramid structures were patterned on the OrmoStamp-coated glass substrate with high fidelity in the first nanoimprint process. In the second nanoimprint process, inverted nanopyramid structures were replicated on the OrmoStamp-coated substrate using the fabricated upright nanopyramid glass substrate as a mold. The replicated inverted nanopyramid structure on resist-coated substrate was faithfully resolved with the high accuracy compared to original Si master mold down to nanometer scale. Both upright and inverted nanopyramid structures can be utilized as surface coatings for light trapping and self-cleaning applications for different types of solar cell and glass surfaces.
Part of the book: Micro/Nanolithography
In this chapter, inverted and upright nanopyramid structures with light-harvesting properties and self-cleaning hydrophobic surfaces suitable for solar cells are presented. Periodic nanopyramid structures with 400–700 nm features were fabricated using interference lithography and combined dry and wet etching processes. The inverted nanopyramids (INP) were applied at the front side of the solar cells using UV nanoimprint lithography. These structures provided effective light-trapping properties and led to oblique angle light scattering and a significant reduction in reflectance resulting in higher power conversion efficiency. The second type, the periodic upright nanopyramid (UNP) structures were applied on a glass substrate by UV nanoimprint process. The glass cover is also utilized as a protective encapsulant front layer. The use of the upright nanopyramid structured cover glass in the encapsulated solar cell has also enhanced the power conversion efficiency due to the antireflection and strong light-scattering properties compared to the bare cover glass. In addition, the upright nanopyramid structured cover glass exhibited excellent self-cleaning of dust particles by rolling down water droplets. These results suggest that the nanopyramid structures with light-harvesting and self-cleaning properties can improve the performance of different types of solar cells, including thin films and glass-based PVs.
Part of the book: Emerging Solar Energy Materials