Optimization of Silicon Heterojunction Interface Passivation on p- and n-Type Wafers Using Optical Emission Spectroscopy

To increase the efficiency in p-type wafer-based silicon heterojunction (SHJ) technology, one of the most crucial challenges is the achievement of excellent surface passivation. Herein, chemical passivation techniques known for n-type technology are successfully applied on p-type float–zone (FZ) wafers, and wafer surface passivation quality is correlated with parameters from plasma diagnostics, namely crystallization rate and electron temperature indices. It is shown that plasma ignition at higher powers than deposition powers enhances effective minority carrier lifetimes τ_eff fourfold for p- (0.6–2.1 ms) and sixfold for n-type (0.6–3.2 ms) wafers while giving opportunity to process under lower electron temperature indices during the nucleation phase. A subsequent hydrogen plasma treatment has a further beneficial effect on chemical passivation, leading to high effective minority carrier lifetimes of 4.5 and 3.1 ms, and implies open-circuit voltages, i-V_OC, of 735 and 720 mV for p- and n-type wafers, respectively. In particular, cell precursors built on p-type wafers demonstrate excellent surface passivation with τ_eff and i-V_OC (4.1 ms and 745 mV). Using these process optimizations, SHJ cells on both p- and n-type wafers are fabricated with efficiencies exceeding 21%.