Transparent conducting oxide-based, passivated contacts for high efficiency crystalline Si solar cells

Abstract

In this work, we investigate a transparent conducting oxide (TCO)-based, passivated contact for the potential use as a passivated tunnel contact to p-type Si. As a surface passivation layer, the Al2O3 films with varying the thickness are deposited using plasma-enhanced atomic layer deposition (PEALD) at 200 °C, followed by post-deposition annealing. For a ∼15 nm thick Al2O3 layer, a high level of surface passivation is achieved, characterized by the effective surface recombination velocity (Seff,max) of <30 cm/s. The samples with ultrathin Al2O3 layer <3 nm, however, shows degradation in passivation quality, reaching the Seff,max<500 cm/s. When Al-doped zinc oxide (ZnO:Al) as TCO contact is directly deposited onto a ∼10.6 nm thick Al2O3 coated p-Si via RF magnetron sputtering, the final passivation quality (p-Si/Al2O3/ZnO:Al) is characterized by the saturation current density at contact (J0,contact) of 92.1 fA/cm2 with the implied open-circuit voltage (iVoc) of 653 mV, showing the passivation quality is not severely degraded after sputtering without thermal treatment. Further process optimization of PEALD is in progress to produce an improved quality of surface passivation with the Seff,max<10 cm/s for ultrathin passivation layers less than 2 nm, enabling a passivated tunneling contact.