Mapping of contact resistance and locating shunts on solar cells using Resistance Analysis by Mapping of Potential (RAMP) techniques

Two new techniques are described, one to locate shunts on solar cells (PRAMP) and one to map the specific contact resistance rc of the front side metallisation (SCRAMP). In addition, the influence of a varying {rho}{sub c} on the diode factor n and the series resistance of a cell was calculated. The new techniques are both based on the mapping of a current induced potential to analyse the resistance problems. The PRAMP scan proved to be an easy technique to detect shunts with a resolution of {approx}1 mm; disadvantage is the impossibility to detect shunts below metal, advantage is the simple equipment that is needed. More important is the SCRAMP scan that can map {rho}{sub c} on a 10 x 10 cm{sup 2} cell in 20 min. Compared to the standard techniques, the advantages of SCRAMP are its speed and the fact that it does not rely on the assumption that {rho}{sub c} is the same for all fingers. The SCRAMP scans showed that screen printed silicon solar cells with low fill factor have large lateral {rho}{sub c} variations. A computer program was written to calculate the influence of these large {rho}{sub c} variations on the I-V curve of a cell. It was found that the diode factor of the cell increases due to {rho}{sub c} variations (even values above 2 can be reached), while the series resistance value does not increase significantly. 5 refs.