Thermally stable poly-Si tunnel junctions enabling next-generation high-efficiency Si solar cells

We demonstrate thermally stable polysilicon (poly-Si)-based tunnel junctions (TJs), that is, n+-poly-Si/p+-poly-Si/SiOx and n+-poly-Si/SiOx/p+-poly-Si/SiOx, for passivating a silicon wafer, selectively extracting holes, and being compatible with the high-temperature firing process of screen-printed metal contacts. An additional interfacial oxide between the n+-poly-Si and p+-poly-Si layers enhances thermal stability and acts as a barrier layer to mitigate dopant interdiffusion between the adjacent poly-Si layers, without significantly increasing the contact resistance. The TJ's thermal stability is investigated by analysing the TJ recombination current density J0 and effective contact resistance ρc after high-temperature firing (740°C to 840°C) of nonmetallised samples. We evaluate two different TJ applications via efficiency potential calculations: (1) When the TJ is applied on the front side of a passivated-contact Si bottom cell for 2-terminal tandem cells, a calculated add-on efficiency of 9.9% for the Si bottom-cell can be achieved with the inclusion of the interfacial oxide; (2) to enable conventional metal screen-printing on a p+-poly-Si layer, the TJ is applied on the rear side of a single-junction Si solar cell, giving a calculated cell efficiency potential of 23.6% at 1-Sun condition. For such a configuration, in the absence of an interfacial oxide between the adjacent poly-Si layers, the cell efficiency potential improves with peak firing temperature. In summary, we successfully develop thermally stable hole-extracting TJs for the two aforementioned applications that are fully compatible with existing industrial silicon solar cell fabrication processes.

Xin Ren Ng and Donny Lai and Puqun Wang and Armin G. Aberle and Rolf Stangl and Fen Lin

Progress in Photovoltaics: Research and Applications

2022

1

10.1002/PIP.3462

1099-159X

1

85-95

John Wiley & Sons, Ltd

30