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

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 (Mg₃(PO₄)₂) is introduced as an electron-selective transport layer (ESTL) for SHJ solar cells. The Mg₃(PO₄)₂ film exhibits a work function (WF) of 3.64 eV and achieves a contact resistivity (ρ_c) of 67.00 mΩ cm² in an n-Si/a-Si:H(i)/Mg₃(PO₄)₂/Al structure, highlighting its potential for effective electron extraction. Performance evaluations reveal that a Mg₃(PO₄)₂/MgF₂ 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 Mg₃(PO₄)₂ is applied to the light-incident side with MgF₂ as the primary anti-reflection coating, the device reaches a PCE of 23.25%. These results demonstrate the effectiveness of Mg₃(PO₄)₂ as an electron-selective material and establish its promise as a ternary compound ESTL for high-efficiency silicon solar cells.