Another important aspect of Solar cell design is the Surface Texturing. Surface texturing, which can be either used in combination with the anti-reflection coating or used by itself, can also be used for minimizing the reflection so as to improve solar cell performance and efficiency. The added roughening to the surface can reduce reflection by the effect of increased chance for the reflected light to bounce back to the surface, instead of reflecting back to the surrounding air.
As explained, Solar cells need it in order to reduce light reflection off its surface, and also in order to enhance light trapping.
An important parameter for surface texturing is the Surface finish or surface topography, which is the shape or nature of the surface as defined by the three different features, surface roughness, lay and waviness. It describes the minor, local abnormalities of a surface from the ideal flat surface.
Different types of techniques used for Surface Texturing
It can typically be achieved in a number of ways. Etchingalong the faces of the crystal planes can be used for texturing the single crystalline substrate. The crystalline structure of silicon leads to a surface which consists of pyramids if the surface is properly aligned with respect to internal atoms. This type of texturing is known as the "random pyramid" texturing and is generally used in the industry of single crystalline wafers.
Chemical process can also be used for the purpose of etching the surface of the solar cell.
One common method for chemical etching is the process in which the Anisotropic wet chemical is used in the formation of pyramids on the (1 0 0) silicon wafer surface by etching back to the (1 1 1) planes.
A different type of surface texturing also used is named the "inverted pyramid" texturing. Using this texturing system, the pyramids are etched downwards into the silicon surface instead of being etched pointing upwards to the direction of the surface.
For multi crystalline wafers, just a small ration of the surface will have the essential orientation of <100> and as a result these texturing techniques are way less effective on the multi crystalline wafers. Yet, different techniques can be used for texturing the multi crystalline wafers, as multi crystalline wafers can be textured using thephotolithographic technique as well as by means of mechanical sculpting of the front surface by the use of lasers or dicing saws to cut the surface into the required appropriate shape.