Approach to the physical origin of breakdown in silicon solar cells by optical spectroscopy

The electrical breakdown of silicon solar cells at low reverse currents has recently gained increased attention. In this study we investigate the physical properties of prebreakdown sites with high resolution spectroscopy techniques. These techniques comprise the measurement of the electroluminescence under reverse voltage, microphotoluminescence spectroscopy, and micro-Raman spectroscopy. The measurements show very high levels of stress at the prebreakdown sites, an increase in the breakdown size with applied reverse bias and redshift in the breakdown electroluminescence spectrum with increasing onset voltage. The results are tentatively explained by a lower bandgap energy at the breakdown sites, which could be caused by stress.