When the method of photoluminescence (PL) is applied, the semiconductor material is excited by a laser beam and the photoluminescence light, which is emitted on recombination of the excited electron-hole pairs, is collected by an optical set-up and analyzed by a spectrometer. Among other quantities, spectrally resolved photoluminescence (sPL) determines the bandgap energy of semiconductor materials and PV absorber layers. It is extremely sensitive to variations of material composition and is therefore an ideal tool for in-line composition monitoring.
Especially in CIGS based thin-film PV production the method is applied to monitor deviations in In/Ga ratio and Cu concentration of the CIGS absorber. The method works even at elevated temperatures of more than 200°C and is hence suitable for composition monitoring directly after the CIGS formation.
LayTec’s PearL is an in-line sPL metrology system, which probes deposited layers typically in less than 0.1 s. It works contact-less and without damaging the sample, thus allowing a fast 100% monitoring in production lines. Learn more on the PearL product page
Metrology methods: overview