Characterising the broadband, wide–angle reflectance properties of black silicon surfaces for photovoltaic applications

Abstract

Black silicon nanotextures offer significant optical performance improvements when applied to crystalline silicon solar cells. Coupled with conventional pyramidal textures, to create so–called hybrid black silicon, these benefits are shown to be further enhanced. Presented here is a comprehensive analysis of different variations of this texture, coupled with typical anti–reflectance schemes such as coated pyramids, with a view to the significance of this on subsequent, real–world, solar energy generation. The study uses an angle–resolved spectrophometry system to characterise and compare the optical properties of these surface textures in terms of reflectance versus wavelength and incident angle, with and without encapsulant layers. This analysis, coupled with time-resolved, location specific irradiance data, leads to a new figure-of-merit, the weighted reflectivity, with which to compare surface textures for use in solar cells. Weighted reflectivity for an encapsulated solar cell surface, averaged over a year, for a Southampton, UK, location is calculated to be 7.6% for hybrid black silicon, compared to 10.6% for traditional random pyramids with a thin film anti–reflective coating.

Properties of Black Silicon Layers Fabricated by Different Techniques for Solar Cell Applications

“…There are numerous studies of the properties of BS with/without passivation films, but they were typically based on one specific fabrication technique. [ 27–32 ] In addition, different experimental approaches and technical means have been used in various studies. Therefore, they are less comparative although there are some nice review articles on different BS materials and/or devices trying to put them together.…”