Electrical characterization of P3 isolation lines patterned with a UV laser incident from the film side on thin-film silicon solar cells

We investigate the properties of P3 isolation lines in a - Si : H / μ c - Si : H solar modules, prepared with a nano-second pulsed UV laser incident from the film side of the solar module. For the electrical characterization of the P3 lines we developed a method which allows us to distinguish between leakage currents directly across the P3 line, leakage currents along the laser line side walls and to monitor changes in conductivity of the TCO underneath the line. We applied the developed characterization method to a series of P3 lines where we systematically varied the used laser parameters. In addition we analyzed selected P3 lines using Scanning Electron Microscopy. From the systematic variation we find that a high leakage current directly across the P3 lines is observed when the back contact is not fully removed. The best P3 lines have the back contact fully removed but an incomplete removal of the silicon in the line. When the silicon layer stack is fully removed in the P3 line we observe an increase in leakage current along the side walls of the laser lines. The best P3 laser line we obtained exhibits a very low leakage current density of only 1.5 μ A cm − 1 at 1 V.