TopCon Solar Cells

BatchTex N

When manufacturing a solar cell, the first step is to texture-etch the silicon wafers, which are sawed but otherwise untreated. To this end, the wafers are separated from the top layer of silicon, which will have been damaged by the sawing, and additives are then used to etch a surface with pyramid-shaped structures that improve light reception. Key factors here are the size of the pyramids and the full coverage that they provide, which results in a low level of reflection. The efficient cleaning of residue from the sawing and texturing processes is also becoming increasingly relevant.
The RENA BatchTex allows this process to be carried out extremely cost-efficiently with throughput rates of up to 14,000 wafers per second and additional, highly effective cleaning measures.

InOxSide Blue

Following texturing, the emitter for the cell is attached by means of diffusion. After it has been diffused in a parasitic process, the emitter needs to be removed from the back of the cell by means of so-called chemical edge isolation, and the etched surface has to be smoothed (“polished”). Cleaning strategies are also playing an ever more important role in this edge isolation process, particularly for advanced cell concepts like TOPCon.
With its InOxSide, RENA boasts years of experience in this segment. Whilst earlier edge isolation systems still used an easily manageable but environmentally and economically questionable mixture of hydrofluoric and nitric acid to perform the etching, the new InOxSide Blue does this completely using environmentally friendly hot potash, without any additives, and achieves an unbeatable polishing quality on the etched surface.
The InOxSide Fusion is a hybrid form that melds both etching strategies. It combines the benefits of acidic and alkaline etching with the ability to adapt the etching process easily to suit different wafer materials. At the same time, it also uses over 50% less nitric acid than the acidic process and produces maximum reflection on the back of the cell.

InPolySide

One unique feature of the TOPCon process is the layer of polycrystalline silicon that it applies, which is used for the electrical passivation of the back of the cell. However, conventional technologies that use LPCVD or PECVD cause a slight “wrapping” during polysilicon plating, which results in the edges and parts of the front side of the cell being covered as well as the back. Before the cell can be processed any further, this wrapping needs to be etched off without damaging any layers beneath.
RENA’s InPolySide removes it using a hot-alkaline etching process that works only on one side. Despite the high temperatures that the hot alkali reaches, the wafer edges are etched with maximum precision, and the wafer is then cleaned.

BatchClean

At certain stages in solar cell manufacturing, particularly before applying electrically passivating layers or prior to high-temperature processes, having separate cleaning steps can make the cell much more efficient.
With their high throughput rates, RENA’s BatchClean systems allow standard or customized cleaning sequences – such as pSC1, SC2, ozone processes, HF/HCI cleaning, and many more – to be carried out extremely efficiently.
Thin silicon oxide layers, which can sometimes be required prior to passivation, can also be applied using the BatchClean BOE and wet chemistry instead of laborious high-temperature processes.