Effective Dielectric Passivation Scheme in Area-Selective Front/Back Poly-Si/SiOx Passivating Contact Solar Cells

Despite the high efficiencies reached by heavily doped poly-Si/SiOx passivating contact solar cells, challenges like the high front parasitic absorption still limit their performance. Previously, we showed a wet etching technique using self-aligned metal grids to remove the front poly-Si in the non-metallized region. Here, we focus on the effective dielectric passivation on this tunneling oxide/n+ in-diffused region. The effect of poly-Si thickness was studied to balance between the passivation quality and the current gain. We then compared various dielectric passivation schemes using SiNx, Al2O3, and stacks thereof via injection-level dependent lifetime and the transfer length method. We demonstrate a SiNx/Al2O3 stack yielded the best passivation performance within device process limitation and obtained an improved front/back poly-Si/SiOx passivating contact device, with a short circuit current density of 41.8 mA/cm2 and an efficiency of 21.8%.