Grain boundary engineering of high performance multicrystalline silicon: Control of iron contamination at the ingot edge

The high performance multicrystalline (HPMC) silicon material with the feature of small and uniform grains has already been widely adopted in photovoltaic industry nowadays. However, the HPMC silicon ingots still suffer a comparatively lower minority carrier lifetime at the ingot edges induced by Fe in-diffusion. Here, we have engineered the grain boundaries (GBs) to control the low carrier lifetime zone at the HPMC silicon ingot edges, based on the grain nucleation enhanced by silicon powder coating at the crucible walls. The resultant GBs with high density paralleling to the crucible walls can getter Fe impurity, and meanwhile become the barriers for Fe diffusion. Therefore, the detrimental effect of interstitial Fe impurity on the carrier lifetime of edge wafers is sufficiently reduced and the performance of corresponding solar cells is improved. The solar cells have a narrower distribution in the performance, which is beneficial for the stability and durability of solar cells and modules. This growth concept using GBs to control the behaviors of Fe diffused from the crucible walls is interesting for photovoltaic application.