Comparison of DLIT- and PL-based Local Solar Cell Efficiency Analysis

Both dark lock-in thermography (DLIT) and photoluminescence (PL) imaging deliver information about the local electronic properties of solar cells. Special methods have been proposed for evaluating DLIT or PL images taken under various conditions with the goal to extract the local two-diode parameters. Knowing these parameters, the locally contributing efficiency data in a cell or local expectation values of the efficiency parameters Voc, FF, or η may be calculated. In this contribution these DLIT- and PL-based approaches are applied to one and the same cell and the results are compared. It is found that both methods lead to similar but not to identical results. The physical reasons for the differences between DLIT and PL based local efficiency analysis are discussed. It is found that the PL-based J02 results are still corrupted by the local series resistance, probably because the simple two-diode model is not sufficient to describe the PL process under electric load with sufficient accuracy. For DLIT this approach is less disturbing.