Dislocation formation during laser processing of silicon solar cell materials



Laser processing, increasingly used for solar cell production, induces defects when choosing inappropriate process parameters. Besides the shape and the pulse energy of the laser, also the surface orientation of silicon substrate has a great influence on the defect formation. By applying a laser beam with a line focus exceeding the critical values such as line width and laser pulse energy, the development of dislocations is observed on (111)-oriented wafers by transmission electron microscopy (TEM). As a result, the formed dislocations are arranged practically parallel to each other in planes parallel to the (111) surface. Their Burgers vectors lie within this plane too. Thus classical concepts of epitaxy hardly explain the dislocation formation. Alternative explanations have to take into account the excessively high temperature close to the melting point, the short time frames given by the laser pulse duration (100 ns) and the not yet analyzed inhomogeneous stress distribution. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)