Rethinking photoluminescence for understanding solar cell degradation

Abstract

Electroluminescence (EL) and Photoluminescence (PL) are powerful tools for characterization of solar cells in the laboratory. While PL is influenced by native defects on the wafers, EL gives also information about solar cell contacts. EL is routinely used for the inspection of solar cells and modules in dark conditions, by using Silicon CCDs. This allows the inspection of a large amount of Silicon modules on-site, thus contributing to ascertain the degradation state of the solar cells without the need to dismount the modules. PL imaging has NOT been used for such inspection tasks of Si solar modules due to the need to excite the entire area of study. We have developed a daylight EL/PL characterization system, by means of an On/Off switch procedure [1]. In the PL configuration mode, excitation is carried out by the Sun light. This also enables on-site PL imaging characterization. However, due to the On/Off procedure, both daylight EL and PL are greatly influenced by the solar cell contacts, being very sensitive to fractures. In this work we compare EL and PL imaging results, both in-lab and on-site, for both solar cells and modules.