‘Solar Module Super League’ (SMSL) member, JA Solar has licensed a number of patents from Shin-Etsu Chemical on doping Ga in silicon crystals and using the Ga-doped p-type crystalline silicon wafers for making solar cells to mitigate the impact of Light Induced Degradation (LID).
Photovoltaic (PV) modules are a general product of the PV industry. PV modules need to be used outdoors. The outdoor reliability of these products is an important quality indicator and light induced degradation (LID) is one of the most intensively discussed reliability indicators.
Today’s industry standard B-doped monocrystalline silicon still suffers from light-induced degradation of the carrier lifetime. Illumination at elevated temperature leads to a so-called regeneration, i.e. a recovery of the carrier lifetime as well as the solar cell efficiency. However, even though the carrier lifetime on test wafers increases from about 1 ms after processing to 3 ms after regeneration, the corresponding PERC+ cell efficiencies in both states are identical. We discuss possible reasons for this discrepancy. Additionally, we evaluate B-doped Czochralski silicon wafers with an ultra-low oxygen content of 2.6 ppma as well as industrial Ga-doped wafers. Both wafer materials are completely LID-free in lifetime measurements and PERC+ cell efficiencies and enable up to 0.4%abs higher efficiencies than present industry-typical boron-doped wafers.
When we visit conferences and industrial players, we are very often surprised at how many responsible scientists for PERC production have never heard about the severe degradation effects that PERC devices can show – in particular when talking about LeTID (Light and elevated Temperature Induced Degradation) alias Carrier Induced Degradation (CID).