Ultralow-work-function lithium oxide (LiO_x) as electron-selective contact for silicon heterojunction solar cell

Dopant-free silicon solar cells have attracted significant interest due to their low cost and simple fabrication. In this work, we investigated a novel electron-selective contact, LiO_x, which exhibits a low work function of 2.39 eV and achieves a contact resistivity of 7.2 mΩ cm² when interfaced with an n-Si substrate. A silicon solar cell featuring a full rear contact structure with LiO_x/Ag achieved an open-circuit voltage (V_oc) of 596 mV and a fill factor (FF) of 80.4%. To further enhance efficiency, we introduced an intrinsic hydrogenated amorphous silicon (i-a-Si:H) layer for surface passivation, along with a thin phosphorus doped amorphous silicon (n-a-Si:H) layer as a transition layer. This approach improved the V_oc to 715 mV and yielded a FF of 78.10%, resulting in a power conversion efficiency (PCE) of 20.62%.