Influence of Very High-Frequency PECVD Hydrogen Plasma Treatment on Intrinsic Amorphous Silicon Passivation Stack: Impact on Silicon Heterojunction Solar Cell Performance

We have investigated the impact of post hydrogen plasma treatment (HPT) using two distinct RF generators operating at 13.56 and 40.68 MHz on the PECVD-deposited i-a-Si:H bilayer stack. VHF-HPT (40.68 MHz) improved the film microstructure, reducing the void fraction to ∼29.9%, compared to ∼34.5% for RF-HPT (13.56 MHz). Consequently, VHF-HPT led to the enhanced minority carrier lifetime to ∼2.7 ms, thereby improving silicon heterojunction solar cell power conversion efficiency to ∼21.31% with an open-circuit voltage of ∼733 mV. In-situ optical emission spectra study of H2 plasma indicated modification in H ions/radicals intensity, which led to enhanced film density and reduced film thickness, further confirmed by spectroscopic ellipsometry analysis. Along with better passivation after VHF-HPT, the hole-selective contact resistivity is also reduced to ∼278 mΩ-cm2 compared to the RF-HPT treatment having ∼378 mΩ-cm2. Dark J-V analysis of cells using a two-diode model revealed that the ideality factor reduced significantly for VHF-HPT, indicating reduced recombination in the space charge region. Finally, the experimental observations are also validated by Sentaurus TCAD numerical simulations by considering i-a-Si:H bulk and c-Si/i-a-Si:H interface defect densities.