Comparison of different techniques for edge isolation

In most industrial type solar cell processes the edge isolation is an important step. After most emitter diffusion techniques, especially the POCl3 diffusion, the front contact is connected with the back contact through the emitter around the edge of the solar cell. As a common technique in industry this shunt is removed by plasma etching of the wafer stack. Other techniques which were investigated are: the grinding of the wafer edge with sandpaper, the cutting of isolation trenches with a wafer dicing saw and the laser separation by inserting trenches, the latter two techniques applied on both sides of the wafer. All these technologies are compared concerning their impact on the solar cell performance of industrial type screen printed solar cells. Using IV measurement (illuminated and dark), laser beam induce current (LBIC) and lock-in thermography it is shown that isolation by laser still suffers from too low fill factors and sawing, grinding, or plasma etching are preferable. A good correlation between decreasing shunt resistance and increasing amount of detected shunts using in-lock thermography or LBIC is found.