Towards industrially feasible high-efficiency n-type Si solar cells with boron-diffused front side emitter - combining firing stable Al2O3 passivation and fine-line printing

In this work we combine the firing stable Al₂O₃ passivation of a boron emitter with an industrially feasible contacting technology to gain a complete front side concept of n-type silicon solar cells with a front side junction. The contact scheme consists of a fine-line printed seed layer, using a silver ink, which is subsequently fired and plated. We studied the contact formation of the applied seed layer on a shallow, industrial-type boron emitter by measuring the specific contact resistance for different firing processes. To gain a deeper insight into the contact formation, SEM micrographs were made from the contact interface. Moreover, the emitter shunting has been studied by firing p⁺nn⁺ test structures at temperatures between 700 and 850 °C. Regarding the passivation of the boron emitter, the firing stability of an Al₂O₃/SiN_x layer stack was investigated on symmetrically processed p⁺np⁺ lifetime samples for the same firing temperature range. Based on these results, p⁺nn⁺ solar cells have been fabricated, featuring a full-area, phosphorous-doped back surface field at the rear. Conversion efficiencies up to 20.5% and fill factors of 80.8% could be achieved, demonstrating the high-efficiency contact formation to the boron-doped emitter.