Enhanced Rear TCO‐Free Heterojunction Crystalline Silicon Solar Cells With MgF _<i>x</i> Electron‐Selective Contact

In silicon heterojunction (SHJ) solar cells, reducing the reliance on transparent conductive oxides (TCOs) is essential for lowering manufacturing costs. Here, we introduce an a‐Si:H( n )/MgF x /Al electron‐selective rear contact to realize a rear side TCO‐free asymmetric device architecture. Ultraviolet photoelectron spectroscopy (UPS) reveals that MgF x possesses a low work function and wide bandgap, enabling favorable band alignment with a‐Si:H( n ) and mitigating Fermi‐level pinning at the metal interface. With an optimized ∼2 nm MgF x layer, the contact resistivity is significantly reduced, and carrier extraction is enhanced through tunneling‐assisted transport. The selective contact yields improved interfacial passivation and supports the formation of an effective n + ‐n junction, resulting in an open‐circuit voltage ( V oc ) of 728 mV and a power conversion efficiency above 21%. These results demonstrate that MgF x is a promising electron‐selective contact material for high‐efficiency, rear‐side TCO‐free SHJ solar cells.