Blocks of different types of Silicon can be observed on this optical image. The presence of non-crystalline silicon leads to reduced conversion efficiency, and due to this, testing crystallinity of silicon in solar cells is important for the manufacture process. Raman spectroscopy can be used for analyses of crystallinity. This application note demonstrates it on the example of a polycrystalline silicon solar cell displayed by Fig.2.
In crystalline silicon the bond lengths are uniform, and as a result there is only one sharp peak at 520 cm-1. In amorphous silicon the bond lengths are varied leading to broad diffuse spectral features around 480 cm-1 (Fig.2). The crystalline fraction is proportional to the intensity ratio of I520/I480. It is possible to see from Fig.2, that different blocks on the polycrystalline silicon cell have different amount of amorphous phase.