Self-Aligned Selective Area Front Contacts on Poly-Si/SiOx Passivating Contact c-Si Solar Cells

Both polarity poly-Si/SiOx passivating contacts in a front/back device configuration may represent the next solar cell architecture after tunnel oxide passivating contacts (TOPCon) cells, but high parasitic absorption in the front poly-Si layer often limits its performance. This work explores a wet etching technique to remove the front poly-Si in the nonmetallized regions using self-aligned metal grids as an etch mask. We systematically examine various dielectric layers (SiNx, Al2O3, and stacks thereof) to study the repassivation of the etched n+ surface, and find that an SiNx/Al2O3 passivation stack can effectively repassivate the etched surface, which we attribute to field-effect passivation from the positive fixed charge from the SiNx layer, and excellent chemical passivation property from Al2O3 in the form of atomic H. We demonstrate a front/back poly-Si/SiOx passivating contact device, with an open-circuit voltage (Voc) of 690 mV, short-circuit current density (Jsc) of 39.8 mA/cm2, fill factor of 78%, and power conversion efficiency of 21.4%. Furthermore, simulations using SunSolve and Quokka 3 show good agreement with both the optical and electrical properties of the experimental device. The power loss analysis reveals improvements in the optical loss from the back Ti adhesion and front SiNx layers would lead to a 23.5% device. Lastly, a techno-economic model compares the production cost of this improved cell with the current TOPCon cells. Our results highlight that further cost reductions in single-sided doped poly-Si layers are needed to compete with mainstream passivated emitter and rear cell, and TOPCon technologies.