Contacting of Busbarless Solar Cells for Accurate I-V Measurements

In recent years, solar cell development has undergone a major change in metallization layout. In their most radical form, busbarless solar cells completely omit the busbar and leave the fingers as solely contacting area. Consequently, characterization and calibration laboratories were forced to develop new contacting units. At the same time, the question of the correct arrangement of current and sense contacts arises. To perform accurate and precise measurements of the current-voltage characteristic of busbarless solar cells, we transfer the well-established concept of busbar-resistance neglecting contacting to the measurement of busbarless cells. The result is a universally valid gridresistance neglecting contacting scheme, which provides the same fill factor as one would get if one had contacted the entire metallized area of the solar cell. We demonstrate that a variety of contacting schemes are able to determine this fill factor if the sensing contact is correctly placed. We provide experimental evidence of consistent results for a contacting with 12 contact bars at ISFH CalTeC and 30 wires at Fraunhofer ISE CalLab, respectively. For the fill factor of 15 silicon solar cells with finger line resistances ranging from 0.6 to 12 /cm we show that the En-values between both calibration laboratories are well below 1, demonstrating a very good agreement within the accompanied measurement uncertainty.