Surface texturing, either in combination with an anti-reflection coating or by itself, can also be used to minimize reflection. Any "roughening" of the surface reduces reflection by increasing the chances of reflected light bouncing back onto the surface, rather than out to the surrounding air.1
Another type of surface texturing used is known as "inverted pyramid" texturing3,4. Using this texturing scheme, the pyramids are etched down into the silicon surface rather than etched pointing upwards from the surface. A photograph of such a textured surface is shown below.
For multicrystalline wafers, only a small fraction of the surface will have the required orientation of <100> and consequently these techniques are less effective on multicrystalline wafers. However, multicrystalline wafers can be textured using a photolithographic technique5 as well as mechanically sculpting the front surface using dicing saws6 or lasers7 to cut the surface into an appropriate shape. A micrograph of a photolithographic texturing scheme is shown below.
The modeling of textured substrates is covered by simulation programs at pvlighthouse.com.au and associated references8
- 1. , “High efficiency silicon solar cells”, in Proceedings of the 14th Annual Power Sources Conference, 1960, p. 22.
- 2. , “United States Patent: 4137123 - Texture etching of silicon: method”. 1979.
- 3. , “Light trapping properties of pyramidally textured surfaces”, Journal of Applied Physics, vol. 62, no. 1, p. 243, 1987.
- 4. , “High performance light trapping textures for monocrystalline silicon solar cells”, Solar Energy Materials and Solar Cells, vol. 65, no. 1-4, pp. 369 - 375, 2001.
- 5. , “Improvements in Silicon Solar Cell Performance”, 22nd IEEE PV Specialists Conference. pp. 399-402, 1991.
- 6. , “Buried contact solar cell”. 1988.
- 7. , “16.7% efficient, laser textured, buried contact polycrystalline silicon solar cell”, Applied Physics Letters, vol. 55, p. 2363, 1989.
- 8. , “Isotextured Silicon Solar Cell Analysis and Modeling 1: Optics”, IEEE Journal of Photovoltaics, vol. 2, no. 4, pp. 457 - 464, 2012.