Extraction of individual-cell photocurrents and shunt resistances in encapsulated modules using large-scale laser scanning

Abstract

Traditional laser scanning of encapsulated thin-film modules yields an optical beam-induced current (OBIC) signal for each cell that is proportional to the product of the cell's shunt resistance and photocurrent. Multiple laser chopping frequencies, ho wever, 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 forward 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)Se2, CdTe, and single-junction amorphous Si modules. Additional measurement at forwa rd bias can be useful for separation of the photocurrent and shunt resistance of cells with very low OBIC signals.