Nano-texturing of multicrystalline silicon
Crystalline silicon is currently the dominant photovoltaics technology, accounting for over 90% of the global PV market. Of this, multicrystalline silicon (mc-Si) accounts for over 60% and is predicted to continue to be an important wafer technology for PV. Traditionally, optical losses in mc-Si solar cells have been reduced using a combination of acid texturing and a thin film antireflection coating. This type of texturing relies on the damage caused by the traditional multiwire slurry wafer sawing (MSWS) technique to initiate the formation of surface features. With the of diamond-wire sawing (DWS) to reduce kerf-loss in wafer production, the saw damage is greatly reduced and so traditional acid texturing is no longer effective. There is therefore a need for texturing methods that can be used on DWS mc-Si wafers to minimise optical losses whilst being compatible with industrial solar cell processes. For this project, you will investigate the use of metal assisted chemical etching (MACE) for texturing of DWS mc-Si wafers to reduce optical losses. This is a technique whereby noble metals with higher electronegativity than Si, such as Au, Ag, and Cu, are used to chemically etch the Si surface through a redox reaction. The resulting nano-textured surfaces are a form of “black silicon” due to their excellent light capturing properties. Explored here are techniques for passivating these highly textured surfaces, followed by a study of the effects of encapsulation of the antireflective surface under polymer and glass layers and examine the light scattering/trapping properties of the structures created. There is also scope for investigating metal contact formation on the nanotextured surfaces, moving towards full cell fabrication and testing. This project will make use of the extensive fabrication and characterisation facilities available at the Southampton Nanofabrication Centre cleanroom facility as well as high performance computing systems to support all experimental investigations with optical and electrical modelling. The project will benefit from the close involvement of Tetreon Technologies Ltd., the UK’s leading manufacturer of industrial tools for fabrication of photovoltaic cells. Tetreon will advise on the industrial compatibility of the processes being developed and assist in development of test equipment.
Jack James Tyson