Collected photocurrent imaging of CIGS solar cells via electro-modulated luminescence under different illumination conditions

The collected photocurrent imaging technique measures the total amount of photocurrent that can be collected from every region of a solar cell. The technique is based on the recently introduced differential photocurrent collection efficiency imaging method, which uses luminescence images taken under varying bias conditions and a constant illumination. The differential photocurrent collection efficiency provides information about how the cell or module current reacts to local changes of the generated photocurrent. We explain in detail how certain assumptions and measurements of the photocurrent collection efficiency under different illumination conditions can extend the differential information we obtain from the differential photocurrent collection efficiency to get information about the total amount of photocurrent collected from each specific region of a solar cell. The method was demonstrated on a thin film Cu(In, Ga)Se ₂ cell, showing quantitatively how series resistance reduce the collection of photocurrent.