Broadband light management using low-Q whispering gallery modes in spherical nanoshells

• Published in: Nature communications 2012-02, Vol.3 (1), p.664, Article 664
• Main Authors: Yao, Yan, Yao, Jie, Narasimhan, Vijay Kris, Ruan, Zhichao, Xie, Chong, Fan, Shanhui, Cui, Yi
• Format: Article
• Language: English
• Subjects: 639/301/357/354; 639/766/400; Electric Conductivity; Electric Power Supplies; Equipment Design; Humanities and Social Sciences; Light; Materials Testing; Microscopy, Electron, Scanning - methods; multidisciplinary; Nanoshells; Nanotechnology - methods; Optics and Photonics; Science; Science (multidisciplinary); Silicon - chemistry; Silicon Dioxide - chemistry; Solar Energy; Sunlight; Temperature
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms1664

Light trapping across a wide band of frequencies is important for applications such as solar cells and photodetectors. Here, we demonstrate a new approach to light management by forming whispering-gallery resonant modes inside a spherical nanoshell structure. The geometry of the structure gives rise to a low quality-factor, facilitating the coupling of light into the resonant modes and substantial enhancement of the light path in the active material, thus dramatically improving absorption. Using nanocrystalline silicon (nc-Si) as a model system, we observe broadband absorption enhancement across a large range of incident angles. The absorption of a single layer of 50-nm-thick spherical nanoshells is equivalent to a 1-μm-thick planar nc-Si film. This light-trapping structure could enable the manufacturing of high-throughput ultra-thin film absorbers in a variety of material systems that demand shorter deposition time, less material usage and transferability to flexible substrates. Control of light absorption in optical devices, such as solar cells, can be achieved through resonant features like whispering gallery modes. Here, these modes are exploited in spherical silicon nanoshells to enhance absorption over a broad spectral range in nanometre-scale flexible layers.