| Popis: |
The emitter sheet resistance Rse on textured silicon wafers is measured by four-point-probe (4PP), eddy-current, and junction-photovoltage (JPV) techniques. In the sample set – manufactured for this study – Rse of diffused n++ and p++ layers and the bulk resistivity ρ of the substrate wafers are all varied to cover the entire range of today’s silicon PV production. It was found, that the 4PP results – from the widely used 4PP sensor with sharp and hard tips – are strongly influenced by the bulk resistivity of the substrate wafers and show poor correlation to the readings of the contactless techniques. In addition, 4PP probes with different tip parameters provide different Rse values. A simple model is proposed to explain the influence of ρ to the measured Rse. This new understanding led to the application of a simple design “soft contact” 4PP sensor, which provides a bulk resistivity independent determination of Rse. Results from the soft-contact 4PP sensor are in excellent agreement with Rse calculated from the eddy-current method. This agreement confirms the accuracy of the soft-probe 4pp technique. Knowing the precise Rse values of all wafers enabled the optimization of the measurement parameters of the recently developed contactless, differential JPV sensor, which is already used in PV production lines. After optimization, the differential JPV measurement was proven to be very precise for the entire sample parameter range. |
