Improvement in the Performance of P-Type Tunnel Oxide Passivated Contact Solar Cell With Selective Tunneling Junctions Underneath the Contacts on Front Side

Industrial silicon solar cells are now moving further from passivated emitter and rear contact (PERC) toward Tunnel Oxide Passivated contact (TOPCon) technology. The efficiency of the PERC solar cell is improved by TOPCon technology, in which the rear side is fully passivated by an oxide/poly-Si tunneling junction. The performance of a TOPCon solar cell may further be improved by the incorporation of selective tunneling junctions underneath the front contacts. Some fabrications have been reported on a similar structure for an n-type Si substrate but they have not achieved the expected results. Also, a detailed study has not been done yet. Using 3-D sentaurus technology computer aided design (TCAD) simulation software, a detailed analysis has been done on the modified structure through the optimization of the tunnel oxides, the interfaces, the n
⁺⁺
poly-Si layer, the selective (SiO
₂
/n
⁺⁺
-poly-Si) tunneling junctions underneath the front contacts, etc., which has not been done earlier. It is seen that a thick n
⁺⁺
poly-Si layer causes parasitic absorption of light, whereas a very thin poly-Si layer cannot provide sufficient field for tunneling of carriers. A thicker tunnel oxide produces a high series resistance, whereas a very thin tunnel oxide cannot restrict the minority carriers to reach to the contacts. Therefore, an optimization is required and the optimization is done based on a fabricated bifacial p-TOPCon solar cell reported in the literature with an efficiency of 21.2% and bulk lifetime of 200 μs. After performing all the modifications in the fabricated reference cell and optimizing different parameters, the efficiency is improved by 3.5% in absolute. The efficiency is further improved to 25.4% with the bulk lifetime of 1 ms.