Light trapping micro and nanostructures fabricated by top down approaches for solar cell applications

Altınoluk, Hayriye Serra
For an ultimate victory of solar energy over polluting fossil fuels, we need to decrease the cost of electricity generated from the sun. The technology based on photovoltaic (PV) solar cell is offering the most promising alternative in this energy conversion. However, this can be possible only if we can reduce the cost of solar cell fabrication and/or increase the conversion efficiency. In order to increase the performance/cost ratio of solar cells, new approaches reducing optical and electrical losses are necessary during the absorption of the light and collection of charge carriers. In this work we focused on the fabrication techniques and the application of various nanostructures on Si surface towards a better light management of the cell surface. The efficiency of a solar cell strongly depends on the properties of the interaction between the incoming light beam and the surface of the device. In order to maximize the absorption and the efficiency of the cell, various light trapping schemes have been proposed. We have applied various lithography techniques such as optical lithography, nanoimprint lithography (NIL), hole mask colloidal lithography (HCL) to generate various nano structures including nano holes patterns. After these pattern transfer process steps, either dry plasma etching or wet chemical etching techniques were applied. For metal assisted chemical etching different metals like silver, gold, titanium were used as the catalyst of the etching. The effect of metal, metal layer thickness, process time and orientation of the wafer were studied. Structural properties of the features like hole diameter, pitch size, depth were varied and optimized. With a variety of texturing and etching process types, at the end of the study, periodic and random-introduced-periodic patterns were successfully implemented to solar cell fabrication step. The performances of the solar cells were investigated both optically and electrically.