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 (Li 3 PO 4 ) /Titanium Dioxide (TiO 2 ) as a new electron selective passivating contact. It is found that the stack achieves an impressive contact resistivity ( ρ c ) of 0.128 mΩ cm 2 on n‐type c‐Si substrates with resistivity ranging from 1 to 3 Ω cm (14.6 mΩ cm 2 for the n‐Si/a‐Si:H/Li 3 PO 4 /TiO 2 /Al contact). Furthermore, it effectively reduces the surface recombination parameter ( J 0 ) to less than 4 fA by incorporating a 6 nm a‐Si:H(i) layer. The characterization of the n‐Si/Li 3 PO 4 /TiO 2 interface reveals that phosphorus diffusion into silicon plays a crucial role in achieving the ultra‐low contact resistivity, while the presence of PO 4 3− 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/Li 3 PO 4 /TiO 2 /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.