730 mV implied Voc enabled by tunnel oxide passivated contact with PECVD grown and crystallized n+ polycrystalline Si

This paper presents the fabrication and optimization of tunnel oxide passivated contact with crystallized n⁺ polycrystalline Si (poly-Si) for high-efficiency large-area n-type front-junction Si solar cells. Starting with a baseline process, we optimized (a) the PECVD deposition precursor SiH₄/PH₃ flow rate, (b) the H₂ gas volume ratio, (c) the crystallization annealing temperature, (d) the tunnel oxide growth temperature, and (e) the deposition power to achieve the highest implied Voc. This resulted in an implied V_oc of 730 mV, J_ob´ of 4.3 fA/cm², and implied fill factor (FF) of >84.5% with symmetric structure on n-type Cz substrate (~4 Ωcm, 170μm), indicating excellent interface passivation quality of tunnel oxide/n⁺ poly-Si contact. Applying a high dose ion-implanted boron emitter passivated with Al₂O₃ and screen-printed and fired Ag/Al front contact, 21.2% cell efficiency was achieved on 239 cm² commercial grade n-type Cz wafers.