EXTRACTION OF INDIVIDUAL-CELL PHOTOCURRENTS AND SHUNT RESISTANCES IN ENCAPSULATED MODULES USING LARGE-SCALE LASER-SCANNING

Traditional laser scanning of encapsulated thin-film modules yields an optical beam-induced current (OBIC) signal for each cell that is prop ortional to the product of the cell's shunt resistance and photocurren t, Multiple laser chopping frequencies, however, if judiciously chosen , can separate the photocurrent and shunt resistance of the individual cells even when electrical access is only available across the entire module, This method of extraction makes no assumptions about the forw ard bias behavior of the cells, requires no time-consuming shading of cells and has the potential to be made semi-automatic. The method has yielded accurate results for CuIn(Ga)Se-2, CdTe, and single-junction a morphous Si modules, Additional measurement at forward bias can be use ful for separation of the photocurrent and shunt resistance of cells w ith very low OBIC signals.