Passivation of Phosphorus Diffused Black Multi‐Crystalline Silicon by Hafnium Oxide (Phys. Status Solidi RRL 12/2017)

Abstract

Black silicon texturing formed by reactive ion etching has great promise in providing strong optical gains for multicrystalline silicon solar cells, especially when coupled with diamond wire sawing. However, the resulting nano-scale surface structures are challenging to passivate with silicon nitride by plasma enhanced chemical vapor deposition, the conventional method used in industry. Researchers from the Australian National University and Trina Solar (see article no. 1700296 by Jie Cui et al.) use hafnium oxide, which contains positive charge, appropriate to passivate the phosphorus diffused surface of solar cells, together with atomic layer deposition, to obtain a conformal coating of the sharp surface features. By optimizing the deposition and annealing conditions, the authors have achieved not only a low surface recombination, but also an effective passivation of bulk defects in multi-crystalline silicon wafers, as shown by photoluminescence imaging. They report a recombination current density of J0n+ = 98 fA cm-2 for the phosphorus diffused black silicon surface, which equates to an attainable open circuit voltage of 691 mV, thus proving that hafnium oxide offers a viable alternative for passivating the surface and the bulk of black-textured multi-crystalline silicon solar cells.