Analysis of the negative charges injected into a SiO 2 /SiN x stack using plasma charging technology for field‐effect passivation on a boron‐doped silicon surface

We investigated field‐effect passivation by injecting negative charges into SiO 2 /SiN x stack using a plasma charge injection technique. The Si/SiO 2 /SiN x samples exhibited a very high flat‐band shift with a high injected negative charge density (>3.0 × 10 13 cm 2 ) after plasma negative charge injection; this density was higher than that for the well‐known Al 2 O 3 layer. Most injected negative charges were present within approximately 90 nm of the surface of the SiN x layer deposited by plasma‐enhanced chemical vapor deposition (PECVD) when comparing the capacitance–voltage analysis results obtained while etching the SiN x film considering four assumptions of the injected negative charge distribution. The saturation current density in a 90‐ohm/sq boron emitter decreased from ~90 to 50 fA/cm 2 after negative charge injection, which is equivalent to the J 0e of the structure passivated with an Al 2 O 3 /SiN x stack. Six‐inch n ‐type bifacial cells with an approximately 100‐ohm/sq boron emitter passivated with SiO 2 /SiN x displayed an approximately 0.2% increase in absolute cell efficiency after negative charge injection. In addition, n ‐PERT bifacial cells with a high boron sheet resistance of ~150 ohm/sq exhibited a 1.0% or higher absolute efficiency enhancement from a relatively low precharging efficiency of approximately 19.0%. We also demonstrated that the final efficiency after charging was comparable with n ‐PERT bifacial cells with Al 2 O 3 passivation, suggesting that the proposed process is a potential low‐cost alternative method that could replace expensive Al 2 O 3 processes.