Imaging physical parameters of pre‐breakdown Sites by lock‐in thermography techniques

Local pre‐breakdown sites in solar cells can be studied by lock‐in thermography (LIT). Three new LIT techniques are proposed and demonstrated here, which are TC‐DLIT for studying the local temperature coefficient of pre‐breakdown sites, Slope‐DLIT for measuring the normalized local slope of the I–V characteristics, and MF‐ILIT for imaging the local carrier multiplication factor. First results on multicrystalline silicon cells show that the pre‐breakdown mechanism cannot completely be described by the conventional impact ionization and internal field emission models.