Art of coloring glass with textures for photovoltaics

Abstract

The characteristic feature of ”thin” film solar cells is that they are thin, ranging over thicknesses of a few micrometers. This results in a drop in the light trapping capability of the solar cell, owing to the Beer-Lambert law. Thus, there is a need to optimize light management to enhance the amount of light being trapped in the photoactive region. This can be done by imparting texture in the glass superstrate to scatter the light and thereby allowing the light to travel over a longer distance in the absorber.

In this thesis, the focus is mainly on developing a high-quality reproducable procedure for achieving periodic texturing in glass and understanding the enhancement in the optical impact of the surface. the first objective was to understand the influence of the different processes involved in the fabrication procedure of periodic textured glass superstrates. This was done by varying the parameters associated with the individual processes and observing the resultant impact on the deterministic characteristics of the texturing process. The influence of the mask design, employed in the photolithography process, on the dimensionality of the texture was also analyzed. Based on the aforementioned results, an optimized recipe was developed and successfully implemented to enhance the depth of the periodic hexagonal texturing imparted onto the glass. Additionally, an indicative parameter Re/P was developed to imply the effect the processes had on the quality of the texturing.

This project also ventured into studying the growth of nanocrystalline silicon on the deep textures developed using the optimized recipe. Following this, an extensive optical analysis of the honeycomb textured superstrates was carried out to realize the scattering effect induced by this texturing on interacting with light. This was done by studying the transmittance components and the angular intensity distribution of the periodic textured glass. The interaction mechanism of the textures was found to be dependent on the wavelength and
the size of the textures. In general, there was a linear increase in the diffuse transmittance with texture height, for all wavelengths of light. However, it was noticed that the slope of this relationship varied for the different wavelengths, since it was mainly dominated by different scattering mechanisms for different wavelengths. Finally, the influence of the optical impact of these hexagonal textures on solar cell performance was also studied by studying the Jsc of the micromorph tandem solar cells, developed on deep hexagonal textures of different periodicities.