Scanning Light Stimulation System With Active Focus Correction at $\mu \hbox{m}$ Resolution for PV Applications

Recently, we introduced a scanning light stimulation system with an automated focus correction. The method is however resolution limited by a CMOS sensor used to focus the light beam. Here, to achieve a higher resolution, we enhanced the light beam focusing process by combining it with an edge detection technique. By this modification, the system resolution is improved down to a 1/e
²
-diameter of 4.3 μm, as demonstrated using an example measurement on a multicrystalline solar cell. Furthermore, it is shown that the obtained resolution is mainly limited by height variations of the positioning system, and methods to compensate these limitations are discussed using example measurements on a quantum well solar cell.