One-step surface wafer damage removal for improved interface passivation in silicon heterojunction solar cells

This work presents an optimisation study of silicon surface preparation for silicon heterojunction solar cells (SHJ) fabricated from surface-damaged wafers, aiming to ensure minimal surface defects and improved passivation at the crystalline silicon-hydrogenated amorphous silicon (c-Si/a-Si:H) interface. KOH etching conditions were optimised to remove diamond-wire-saw (DWS) damage on c-Si while tuning nanoscale faceting for improved interface passivation. Namely, KOH 45% was used to smooth the surface and remove saw damage, while KOH 5% generated approximately 20 nm pyramidal-like features in a single-step, IPA-free process. For the fabrication of SHJ solar cells with an Aluminium Back Surface Field (Al-BSF), intrinsic and n-type doped a-Si:H layers were deposited by plasma-enhanced chemical vapor deposition (PECVD) on the front side of the devices. Two different (i)a-Si:H films, one dense, deposited with 50% hydrogen dilution, (i d )a-Si:H, and the other, under-dense, using pure silane gas, (i ud )a-Si:H, were used in different solar cells. A relative improvement of 18% in implied PCE (Suns-Voc) was observed for KOH 5% with dense (i d )a-Si:H versus KOH 45%, which was attributed to the effect of nanoscale faceting created on the c-Si surface by the KOH 5% treatment.