Electroluminescence (EL) and Photoluminescence (PL) are the two core optical inspection technologies in photovoltaic manufacturing. While both capture luminescence images to reveal defects, they serve fundamentally different purposes.
EL Testing (Electroluminescence)
EL testing requires applying forward bias current to a solar cell or module. The device emits near-infrared light, which is captured by a sensitive camera. EL reveals microcracks, broken cells, cold solder joints, broken grids, PID degradation, and cell efficiency variations.
EL is primarily used for finished cells, modules, and field inspection.
PL Testing (Photoluminescence)
PL testing uses an external light source to excite the semiconductor material. No electrical contact is needed. PL detects crystal defects such as dislocations and grain boundaries, impurity distribution, minority carrier lifetime, and process uniformity.
PL is ideal for raw wafers and in-process monitoring.
When to Use Each
The simple rule: PL checks material quality, EL checks product quality. A comprehensive quality system uses both technologies at appropriate stages of the manufacturing chain.