Passivation of Phosphorus Diffused Black Multi‐Crystalline Silicon by Hafnium Oxide

Abstract

A key challenge for the success of the recent trend to adopt diamond wire sawing for multi‐crystalline silicon wafers is the texturing and passivation of their surfaces. The various so‐called “black silicon” texturing technologies show great promise in providing strong optical gains, but the nano‐scale surface structures resulted from dry etching are challenging to passivate with the conventional plasma enhanced chemical vapor deposition of silicon nitride. In this work, a single layer of atomic layer deposited hafnium oxide, in combination with a short anneal, has been used to demonstrate not only low surface recombination on reactive ion etched and phosphorus diffused (90 Ω/□) surfaces but also effective passivation of bulk defects in p‐type 1.5 Ω cm multi‐crystalline silicon wafers. A combination of photoluminescence imaging and quasi‐steady state photoconductance measurements shows that the recombination via bulk defects such as grain boundaries is mitigated due to hydrogenation during rapid thermal annealing at mid to high temperatures in nitrogen. A further activation anneal at low temperature following hydrogenation improves the effective carrier lifetime by 40%. A recombination current density of J0n+ = 98 fA cm−2 per side at an injection level of Δn = 1015 cm−3 has been obtained, which equates to an attainable 1‐sun implied open circuit voltage of 691 mV when bulk and rear surface recombination are excluded. These results prove that hafnium oxide offers a viable alternative for passivating the surface and the bulk of multi‐crystalline silicon solar cells.