Towards the efficiency limits of multicrystalline silicon solar cells

In this contribution, we present our recent results for high efficiency multicrystalline silicon solar cells. Based on n-type high-performance multicrystalline silicon substrates in combination with the TOPCon solar cell concept featuring a full area passivating back contact and a boron-diffused emitter as well as a plasma-etched black silicon texture at the front side, a certified conversion efficiency of 22.3% has been achieved, which is currently the world record efficiency for multicrystalline silicon solar cells. A detailed loss analysis of the record solar cell batch discloses the nature of the remaining loss mechanisms, revealing the route for further improvements. We observe an efficiency gap between the multicrystalline and the FZ reference solar cells of similar to 1%(abs). Compared to the FZ reference cells, the me-Si cells also feature a significantly larger scattering in V-oc and J(sc) well as a fill factor loss of similar to 1.5%(abs). We show that the scattering in J(sc) correlates with the area fraction of recombination active structural crystal defects and the scattering in V-oc additionally with lateral emitter-induced in-homogeneities. The fill factor loss is attributed to the general presence of strongly recombination-active grain boundaries. A detailed loss analysis of the record me-Si solar cell shows that the major electrical losses are due to recombination at grain boundaries (0.7%(abs)) and recombination in the emitter (0.6%(abs)). By reducing these electrical loss channels, e.g. by an improved crystallization process together with a hydrogenation of the bulk and application of an adapted emitter, we expect to reach efficiencies for me-Si solar cells in the range of 23%.