Silicon solar cells: Fast anneal fights defects

Sol. Energy Mater. Sol. Cells http://doi.org/bj7m (2016)

Multicrystalline silicon solar cells — enjoying a photovoltaic market share of 65% — are affected by defect-induced degradation, which curbs device performance and is particularly severe in the so-called passivated emitter and rear contact (PERC) architecture. The exact nature of the defects causing the degradation, which can take years to develop under normal operating conditions, is unclear; however, it can be investigated by accelerating the degradation by subjecting the cells to high temperature and light irradiation for a few hundred hours. David Payne and colleagues at the University of New South Wales now show that the degradation can be reduced 80% by using a 10 second annealing treatment at 200 °C under illumination with a high intensity of 44.8 kW m⁻². The annealing likely induces a passivation of the defects causing the degradation.

Credit: © PABLO BLAZQUEZ DOMINGUEZ / STRINGER / GETTY IMAGES NEWS / GETTY IMAGES

The research team first confirm that the degradation occurs also under carrier injection in the dark, and it is thus generated by excess carriers rather than directly by light. Then they compare degradation in PERC cells from different commercial manufacturers and from wafers at different positions on the same silicon ingot, concluding that there is great variability among manufacturers and positions along the ingot. Finally, the team tested the effects of rapid passivation treatments with varying time and temperature while monitoring cell stability. The rapid annealing significantly reduced degradation after 225 hours of light-soaking at high temperatures compared to control samples.