Potential of chemical rounding for the performance enhancement of pyramid textured p-type emitters and bifacial n-PERT Si cells

We have investigated the effects of chemical rounding (CR) on the surface passivation and/or antireflection performance of AlO_x- and AlO_x/SiN_x:H stack-passivated pyramid textured p⁺-emitters with two different boron doping concentrations, and on the performance of bifacial n-PERT Si solar cells with a front pyramid textured p⁺-emitter. From experimental results, we found that chemical rounding markedly enhances the passivation performance of AlO_x layers on pyramid textured p⁺-emitters, and the level of performance enhancement strongly depends on boron doping concentration. Meanwhile, chemical rounding increases solar-weighted reflectance (R_SW) from ～2.5 to ～3.7% for the AlO_x/SiN_x:H stack-passivated pyramid textured p⁺-emitters after 200-sec chemical rounding. Consequently, compared to non-rounded bifacial n-PERT Si cells, the short circuit current density Jsc of 200-sec-rounded bifacial n-PERT Si cells with ～60 and ～100 Ω/sq p⁺-emitters is reduced by 0.8 and 0.6 mA/cm², respectively under front p⁺-emitter side illumination. However, the loss in the short circuit current density Jsc is fully offset by the increased fill factor FF by 0.8 and 1.5% for the 200-sec-rounded cells with ～60 and ～100 Ω/sq p⁺-emitters, respectively. In particular, the cell efficiency of the 200-sec-rounded cells with a ～100 Ω/sq p⁺-emitter is enhanced as a result, compared to that of the non-rounded cells. Based on our results, it could be expected that the cell efficiency of bifacial n-PERT Si cells would be improved without additional complicated and costly processes if chemical rounding and boron doping processes can be properly optimized.