Observation of Polycrystalline Solar Cell Using a Laser-SQUID Microscope

Laser-SQUID microscopy is a technique for nondestructive inspection of the electrical properties of semiconductors. In laser-SQUID microscopy, a photocurrent is induced by a laser with an energy larger than the band gap of the semiconductor sample. The magnetic field induced by this photocurrent is detected by a SQUID. In our experiment the laser was focused on the surface of the sample, and a high-temperature superconducting SQUID was positioned behind the sample to detect the magnetic field from the photocurrent. The sample was raster scanned while the relative position of the SQUID and laser spot was fixed. The sample used was a commercially available polycrystalline silicon solar cell containing a p-n junction. It had several line electrodes and a transport electrode layer on the surface, and the reverse side was covered with a metal electrode. We studied a piece of this polycrystalline solar cell using a 1065 nm laser. Magnetic field induced by the laser was observed successfully. The produced image shows the inhomogeneity of the solar cell.