Optimization of rear surface morphology for industrial tunnel oxide passivated contact solar cells

We aim to improve cell efficiency by developing optimal rear surface morphology for industrial tunnel oxide passivated contact (TOPCon) solar cells. Using a new chemical additive in the rear side polishing process, the pyramid base size can be increased from 2 to 10 μm to achieve a relatively flat surface for passivation improvement. As a result, the wafer minority carrier lifetime under new chemical additive condition measured at 5E15 cm−3 injection density by the Sinton WCT-120 tool was increased from 1865 to 3043 μs, and the implied open circuit voltage (iVoc) was also improved from 731.6 to 748.0 mV by comparing with the baseline of standard cell production (G1). The better passivation is due to the decreased surface recombination rate and more uniform passivation layer. However, the contact resistance was increased from 1.01 to 1.11 mΩ·cm2, which will result in a lower fill factor of TOPCon solar cells. To solve this contact problem, one more texture process was used to generate many small pyramids (1 μm size) on the larger pyramid bases. The contact resistance was successfully decreased from 1.11 to 0.87 mΩ·cm2. To check the final cell performance, TOPCon solar cells with different rear surface morphologies were also fabricated in the industrial mass production line. By comparing with the baseline of G1, our technology can increase the cell efficiency by 0.24% absolutely, and this technology can be applied to cell production directly.