Self‐Diffusion Effect Assisted TiO₂/Li₃PO₄ Electron Selective Passivating Contact in Silicon Solar Cells Approaching 23% Efficiency

Abstract Carrier selective contacts with passivation effects are considered to have a significant influence on the performance of crystalline silicon (c‐Si) solar cells. It is essential for electron selective contact materials to meet the requirements of ultra‐low contact resistance and excellent passivation effects. This work introduces a stack layer of Lithium Phosphate (Li₃PO₄) /Titanium Dioxide (TiO₂) as a new electron selective passivating contact. It is found that the stack achieves an impressive contact resistivity (ρ_c) of 0.128 mΩ cm² on n‐type c‐Si substrates with resistivity ranging from 1 to 3 Ω cm (14.6 mΩ cm² for the n‐Si/a‐Si:H/Li₃PO₄/TiO₂/Al contact). Furthermore, it effectively reduces the surface recombination parameter (J₀) to less than 4 fA by incorporating a 6 nm a‐Si:H(i) layer. The characterization of the n‐Si/Li₃PO₄/TiO₂ interface reveals that phosphorus diffusion into silicon plays a crucial role in achieving the ultra‐low contact resistivity, while the presence of PO₄³⁻ groups helps in fixing hydrogen atoms to maintain the desired chemical passivation effect. Finally, a silicon heterojunction solar cell (SHJ) with a rear full‐area configuration of a‐Si:H/Li₃PO₄/TiO₂/Al is successfully demonstrated achieving an impressive power conversion efficiency of 22.89%. The result proves the efficacy of employing hydrogen‐rich low‐work function metal oxide stacks as electron selective passivating contacts.