Mechanical wafer engineering for high efficiency solar cells: an investigation of the induced surface damage

During mechanical structuring of crystalline silicon an electronically active surface damage layer is induced whose complete removal is a prerequisite for the preparation of highly efficient mechanically textured multicrystalline silicon solar cells. In order to evaluate the presently unknown damage layer thickness of mechanically textured silicon, electron microscopy studies and microwave reflection lifetime measurements in combination with a step etching procedure were performed using mono and multicrystalline silicon as base material. The influence of the diamond grain size and the lateral cutting speed of the beveled sawing blades on the surface damage was studied to obtain a better understanding of the mechanical structuring of silicon. In order to confirm the results obtained from lifetime measurements, screenprinted mechanically V-grooved solar cells were processed with different etching times during the sawing damage removal process step. It could be shown that the electronically active surface damage layer has a thickness of about 3 /spl mu/m when applying standard grooving parameters and a diamond grain size of 4-6 /spl mu/m within the abrasive.