High resolution inline detection of changes in the conduction type of multicrystalline silicon by contact less photoconductivity measurements

Changes in the conduction type of a multicrystalline brick can occur, since a high phosphorus concentration is typical for the low quality feedstock that is usually used in PV industry. The inline detection of these changes is made possible via photoconductivity measurements. The measured photoconductivity depends strongly on the resistivity of the sample. With a developed computer algorithm the sharp raises of the photoconductivity at pn-changes can be detected in bricks. With these measurements it is possible to detect pn-changes with a one mm resolution as early as possible in the production process.