A nondestructive technique to test silicon wafer solar cells could lead to higher solar cell efficiency and improved yield for photovoltaic panel manufacturers. An Andor Luca-R EMCCD camera images a solar module (1000 × 450 mm.(Image: Andor Technology) Scientists at the National University of Singapore are developing methods of characterizing solar cells based on luminescence detection and are relating the technique to the electrical properties of the devices. They are using Andor Technology plc’s Luca-R electron-multiplying CCD (EMCCD) camera to image the solar cells and believe the method may be integrated into the production process. “We have shown that, by controlling the applied voltage inducing electroluminescence in solar cells, the observed spectrum of emitted radiation may be used to identify [and study] particular performance-reducing defects,” researcher Matthew Peloso said. He said the method has proved useful at the module and cell levels. “We demonstrated that breakdown luminescence — which we believe is associated with metallic impurities — does not show a one-to-one relationship with other defect-related luminescence signals detected at energies below the silicon bandgap. Interestingly, certain defects did not lead to electrical shunts, which may cause irreversible destruction of PV modules and cells.” The researchers chose the Luca-R camera because of its high red to NIR sensitivity and linear response to intensities, which allow more quantitative data acquisition. The EM gain control enabled them to enhance signal to noise when necessary, although they operated much of the time in non-EM gain mode. The research is detailed in the paper “Observations on the Spectral Characteristics of Defect Luminescence of Silicon Wafer Solar Cells,” published in the 2010 Photovoltaic Specialists Conference (PVSC) proceedings. For more information, visit: www.andor.com