Preparation of poly-Si Based Passivating Contact for TOPCon Solar Cells

The TOPCon pilot line at Fraunhofer ISE was established a few years ago. It has been introduced in detail in its present form by Mack et al. in 2022 [1] and is being improved constantly. The PVTEC Frontend laboratory, for example, is currently upgraded making Fraunhofer ISE one of the first European research institutes to be able to handle wafers in M10, later also G12, format. The maximum certified conversion efficiencies reach 24.5% for M2 and 24.0% for M10 wafer size. Thus, it is an ideal platform to gain a deeper understanding about the different physical mechanisms in TOPCon solar cells and to evaluate innovative technologies in an industry-like environment. The structure and the process steps for the preparation of industrial TOPCon solar cells, also referred to as "iTOPCon", are summarized in Figure 1. There is a broad agreement on most technologies applied for each process step in research and industrial manufacturing. However, a variety of technologies is used to prepare the TOPCon contact itself at the rear of the solar cell which consists of an ultra-thin interfacial oxide SiOx and a highly doped polycrystalline silicon (poly-Si) layer. This manuscript reviews the current research status with regards to the preparation of poly-Si based passivating contact for TOPCon solar cells at Fraunhofer ISE. To this end, different deposition technologies for both interfacial oxide as well as poly-Si layers are introduced and evaluated. Furthermore, it gives an outlook for possible advancements related thereto such as local p-type passivating contacts at the front side of TOPCon or TOPCoRE (TOPCon rear emitter) solar cells.