Determination of Current Transport Efficiency Map by Optoelectronic Reciprocity Relation in CdTe Solar Cells

Transport efficiency (f
_T
) maps of photon-generated current from the junction to the terminal are demonstrated in CdTe solar cells, based on luminescence images and a recent reciprocity theorem. Current transport efficiency maps directly reveal the local electrical losses distribution at different working points, which help to understand the main detrimental mechanisms in CdTe cells. Electroluminescence and photoluminescence imaging measurements are used to distinguish and discuss the localized defects as well. The validity of this luminescence-derived method is successfully verified by comparison with simulation and standard electrical measurements. The diode-like shunts, which rob currents from nearby areas, cause significant decreases of local f
_T
, while the effect of series resistance depends on the terminal current and dominates the additional applied voltage when operating over VOC.