Zinc Sulfide Enabling Remarkable Surface Passivation of Crystalline Silicon

Abstract

The development of future crystalline silicon (c-Si) solar cell technologies requires innovative surface passivation layers. Sulfides are a somewhat unexplored class of passivation materials, despite previous reports showing that sulfurization of the c-Si surface enhances surface passivation. Herein, we report a novel transparent passivation stack composed of ZnS/Al2O3, sequentially deposited by atomic layer deposition (ALD). This stack exhibits remarkable surface passivation, reaching a recombination current pre-factor J0 as low as 1.0 fA/cm2 and implied open-circuit voltages iVoc > 730 mV for a wide range of deposition and annealing conditions. Capacitance–voltage measurements reveal an extremely low interface state density of ≈ 1×1010 cm−2 eV−1, on par with state-of-the-art Si-based passivation layers such as SiO2 and a-Si:H, together with a moderate positive fixed charge. A close lattice match between c-Si and ZnS suggests potential epitaxial growth, which could explain the low interface state density and outstanding surface passivation, despite the observation of a polycrystalline bulk structure. These results establish ZnS as an important new material for c-Si surface passivation, with the potential to enable future innovations either as an interlayer for passivating contacts or as a dielectric passivation layer in c-Si solar cells.