Room-temperature FT-luminescence analysis of Cu(In,Ga)Se2 films and devices

The authors report a rapid, convenient luminescence technique for quality control of polycrystalline Cu(In,Ga)Se₂ (CIGS) films and photovoltaic (PV) devices. The speed and convenience of the luminescence analyses were realized by using a Fourier transform (FT) Raman spectrophotometer which operates in the near-infrared (NIR) spectral region encompassing the band gap and defect levels of CIGS. With minor modifications to the FT-Raman spectrophotometer, the authors were able to detect both photoluminescence (PL) and electroluminescence (EL) from CIGS devices at room temperature. The FT-EL technique allows luminescence measurements to be made using this equipment at energies up to 1.3 eV, while the FT-PL technique is limited to energies below 1.15 eV. By increasing sensitivity and eliminating the need for sample cooling, this approach reduced the measurement time by an order of magnitude relative to comparable dispersive PL measurements. They used a fiberprobe accessory to the FT-Raman spectrophotometer to demonstrate that samples can be checked for uniformity at remote locations, e.g. online, using FT-PL spectroscopy. They also used a microscope accessory to obtain the PL spectra of visibly discolored regions some tens of microns in diameter on a CIGS device, and to show that these regions emit PL at significantly lower energy and intensity than nearby uniform regions of the device