Silicon based core-shell silicon nanowires for broadband and wide angle antireflection
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Silicon based core-shell silicon nanowires for broadband and wide angle antireflection
P. Pignalosa1, 2, H. Lee3, W. Guo2, X. Duan4 and Y. Yi2, 1, 4* 1
New York University, New York, NY City University of New York, SI/GC, New York, NY 3 Beijing University of Science and Technology, Beijing 4 Massachusetts Institute of Technology, Cambridge, MA 2
ABSTRACT Antireflection with broadband and wide angle properties is important for a wide range of applications on photovoltaic cells and display. The SiOx shell layer provides a natural antireflection from air to the Si core absorption layer. In this work, we have demonstrated the random core-shell silicon nanowires with both broadband (from 400nm to 900nm) and wide angle (from normal incidence to 60ยบ) antireflection characteristics within AM1.5 solar spectrum. The graded index structure from the randomly oriented core-shell (Air/SiOx/Si) nanowires may provide a potential avenue to realize a broadband and wide angle antireflection layer. *e-mail: [email protected]
INTRODUCTION For next generation photovoltaic cells, one of the key challenges for further development is how to achieve broadband and wide angle antireflection at the front surface within the AM1.5 solar spectrum. With the rapid progress of nanotechnology, many nano scale photonic devices as small as 30nm have been realized, which are very promising to achieve manipulation of photons at chip scale and having broad applications in renewable energy (photovoltaic cells, solid state lighting), telecommunications and bio medical field1. A number of methods for enhancing optical absorption have been proposed, including the use of dielectric photonic structures2-18 or plasmonic metallic nanoparticles19-21. Silicon nanowires (SiNWs) have attracted extensive interests because of its potential applications in future nanoscale renewable energy devices. Many SiNWs have been fabricated by various techniques, such as the Vapor-Liquid-Solid (VLS) method22-24, Template-based methods25-26, lithography27 and nanoelectrochemistry method28. Low reflectance SINWs has also been demonstrated29-30. In order to realize the broadband and broad angle antireflection, graded index nanowires with high index Si as core layer, low index SiOx as cladding layer, and randomness are showing promises31-32. RESULTS In this work, we have demonstrated SiNWs with a core-shell structure using VLS method which has potential for large area photovoltaic cell applications. The VLS is a
successful method that is applied in SiNWs. The core-shell structure shows good light trapping property at wide range of visible light and broad angle, as the graded index from the core-shell (Si/SiOx) nanowire structure provides natural antireflection characteristics. Present SiNW works on photovoltaic field are largely focused on how to fabricate aligned and ordered nanowire arrays to increase device efficiency33, although the high costs associated with complicated process makes it difficult to apply in large scale. Here, we introduce a structure that can be produced in
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