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 AlOx- and AlOx/SiNx: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 AlOx 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 (RSW) from ∼2.5 to ∼3.7% for the AlOx/SiNx: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.