n-Type polysilicon passivating contact for industrial bifacial n-type solar cells

We present a high-performance bifacial n-type solar cell with LPCVD n+ polysilicon (polySi) back side passivating contacts and fire-through screen-printed metallization, processed on full area 6″ Cz wafers. The cells were manufactured with low-cost industrial process steps yielding a best efficiency of 20.7%, and an average Voc of 674 mV. We analysed effects of variation of doping level, thickness, and oxide properties of the n-type polySi/SiOx layers, as well as hydrogenation from a PECVD SiNx:H coating, which led to recombination current densities down to ~2 fA/cm2 and ~4 fA/cm2 on planar and textured surface, respectively. Analysis shows that the wafer bulk lifetime in the cell is high and that the Voc of the cell is limited by the Jo of the uniform diffused boron emitter and its contacts. Ways to improve the efficiency of the cell to >22% are indicated.