Zinc Sulfide Enabling Remarkable Surface Passivation of Crystalline Silicon

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/Al 2 O 3 , sequentially deposited by atomic layer deposition (ALD). This stack exhibits remarkable surface passivation, reaching a recombination current pre‐factor J 0 as low as 1.0 fA/cm 2 and implied open‐circuit voltages i V oc > 730 mV for a wide range of deposition and annealing conditions. Capacitance–voltage measurements reveal an extremely low interface state density of ≈ 1×10 10 cm −2 eV −1 , on par with state‐of‐the‐art Si‐based passivation layers such as SiO 2 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.