A strong-oxidizing mixed acid derived high-quality silicon oxide tunneling layer for polysilicon passivated contact silicon solar cell

We developed a new wet-chemical method to grow the high-quality tunnel silicon oxide (SiO_x) layer by using a strong-oxidizing mixed acid, which consists of three volumes of HNO₃ (68 wt%) and one volume of H₂SO₄ (98 wt%), named as the CNS (concentrated nitric and sulfuric) acid for short. In comparison with the HNO₃ acid, the CNS acid grows high-quality SiO_x layer with the higher oxidized state at 60 °C, where the relatively low temperature avoids the significant volatilization of acid and remains the quality of acid during the extending process. The results prove that the SiO_x grown in the CNS acid benefits for the surface passivation of the n-type polysilicon passivated contact structure. An average gain of implied open circuit voltage (iV_oc) by 2–10 mV and a reduction of single-side surface saturated dark current (J₀) by 1–7 fA/cm² are obtained by using the 60 °C CNS-acid grown SiO_x to replace the 60 °C HNO₃-acid grown one. Also, in comparison with the 90 °C HNO₃ acid, the 60 °C CNS acid exhibits improved stability and repeatability for preparing the SiO_x during the extending process. The CNS-acid grown SiO_x helps the polysilicon passivated contact solar cell to raise the efficiency by ~ 0.15% on average. In summary, the CNS acid has shown the potential for industrial application, which improves not only the manufacturing process but also the device performances.