High‐Efficiency Silicon Heterojunction Solar Cells Enabled by a Mg ₃ (PO ₄ ) ₂ /MgF ₂ Stack with Over 23% Power Conversion Efficiency

Abstract Dopant‐free silicon heterojunction (SHJ) solar cells offer several advantages over conventional designs, including lower equipment costs, simplified processing, and reduced parasitic absorption. These benefits have made dopant‐free SHJ architectures an area of growing research interest. In this study, magnesium phosphate (Mg ₃ (PO ₄ ) ₂ ) is introduced as an electron‐selective transport layer (ESTL) for SHJ solar cells. The Mg ₃ (PO ₄ ) ₂ film exhibits a work function (WF) of 3.64 eV and achieves a contact resistivity ( ρ _c ) of 67.00 mΩ cm ² in an n‐Si/a‐Si:H(i)/Mg ₃ (PO ₄ ) ₂ /Al structure, highlighting its potential for effective electron extraction. Performance evaluations reveal that a Mg ₃ (PO ₄ ) ₂ /MgF ₂ stack outperforms individual layers. A full‐rear‐contact SHJ solar cell incorporating this stack achieves a power conversion efficiency (PCE) of 22.88%. Furthermore, when Mg ₃ (PO ₄ ) ₂ is applied to the light‐incident side with MgF ₂ as the primary anti‐reflection coating, the device reaches a PCE of 23.25%. These results demonstrate the effectiveness of Mg ₃ (PO ₄ ) ₂ as an electron‐selective material and establish its promise as a ternary compound ESTL for high‐efficiency silicon solar cells.