Decreasing the resolution limit of laser beam induced current measurements below the beam size without confocal optics: Determining laser scribe widths

Abstract

Here, we report a method using laser beam induced current (LBIC) measurements to ascertain nonresponsive features of photovoltaic devices that are smaller than the measurement beam size. To demonstrate the method, we determine the effective electrical width of laser scribed lines. Laser scribing is a critical process in producing thin-film photovoltaics modules and minimizing the effective width of the laser scribed lines is important for closing the cell-to-module efficiency gap. However, in addition to removing material, laser scribing can also produce a heat-affected zone in which the optoelectronic properties of the remaining materials may be adversely impacted. We measured the LBIC signal across scribe lines that were produced in CdTe thin-films. The collected data was compared with the expectations based on the probing beam's shape and the profile of the scribed line. The approach allows the electrical dead width to be determined with a resolution that is substantially higher than the width of the LBIC beam. At the lowest scribing powers, where the lines were the smallest, the electrically-determined widths were larger than the optically-determined widths by nearly a factor of two. The ability to rapidly resolve features that are much smaller than the dimensions of the probing laser beam without the use of confocal optics may be useful in a manufacturing environment, as demonstrated here, or more generally for rapid defect identification on devices with areas ranging from centimeters up to meters.