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 (ρc) of 0.128mΩcm2 on n-type c-Si substrates with resistivity ranging from 1 to 3Ωcm (14.6mΩcm2 for the n-Si/a-Si:H/Li3PO4/TiO2/Al contact). Furthermore, it effectively reduces the surface recombination parameter (J0) to less than 4fA by incorporating a 6nm 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 PO4 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/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.