Fabrication of Silicon Hierarchical Structures for Solar Cell Applications

Hierarchical silicon structures consisting of micropyramids and nanowire arrays are fabricated by two-step chemical etching processes aimed at achieving cost and time effectiveness constraints without using any expensive vacuum system or complicated lithography process. The hierarchical structures can suppress the average reflectance to as low as 4.3% from 300 to 1100 nm without causing poor minority carrier lifetimes, exhibiting excellent broadband light-harvesting abilities with minimal recombination losses, which is the key point to design high-performance nanostructured solar cells. By utilizing hierarchical structures in the practical solar cells application, the short-circuit current density (J(sc)) shows a significant enhancement from 21.5 to 28.7 mA/cm(2), and the conversion efficiency is enhanced by a factor of 35%. Such a significant enhancement is attributed not only to the superior light harvesting achieved by hierarchical structures but also to the benefit of small electrical losses in the solar cells. Thus, the concept and technique presented in this paper open avenues for developing high-performance structure solar devices.