Texturing remains a core wet-bench step, typically combined with saw-damage etching and relying on alkaline chemistry for monocrystalline wafers
Additives have become essential in modern texturing, improving homogeneity, reducing foaming, and enabling better process control across variable wafer quality
Tailored additive formulations like RENA’s MONOTEX series are delivering measurable efficiency improvements in TOPCon and HJT cells, with independent validation from research institutes
Texturing, often combined with SDE, remains a key application of wet benches in solar cell manufacturing. While SDE aggressively removes the outer silicon layer, texturing involves controlled etching to minimize light reflection. Today, texturing primarily relies on alkaline chemistry, which is well suited for monocrystalline wafers. Acidic solutions, once common during the high-volume production of multicrystalline wafers, have largely disappeared. The choice of chemistry also influences the mode of processing: alkaline texturing is typically performed in batch systems, while acidic solutions, which enable higher etching rates, support faster inline processing. As a result, wet-chemical benches for SDE and texturing are predominantly batch-based today. However, SCHMID is somewhat special in this context. The company has optimized inline alkaline tools to deliver precise frontside texturing with minimal rear-side interference. Inline systems offer better compatibility with automation setups, especially for thinner wafers.
The ultimate goal of this wet-chemistry station is to create a pyramid-like structure on the emitter side of the silicon to reduce reflectivity and enhance absorption. The pyramid size plays a crucial role in achieving this. In the previous survey, RENA reported that the optimal pyramid size is around 1 μm. However, Michael Vees, Sales Director Solar, RENA Technologies GmbH, points out that the ideal size is closely linked to passivation quality. In trials conducted with a research institute, the company tested uniform pyramids of about 5 µm and, surprisingly, these larger pyramids delivered higher cell efficiency compared to smaller ones. While the efficiency gain was an unexpected side effect, it clearly highlights the criticality of process chemistry to solar cell performance. The key, Vees explains, was optimizing the additives (see Surface Processing For TOPCon, HJT & BC Solar Cells).
Additives are the most important ingredients in the texturing recipes, and their formulations are often proprietary. They help achieve homogeneity and facilitate etching the surface more evenly in a short time. Looking back, the early generation of additives contained large amounts of IPA. Then the industry evaluated various compositions, including inorganic salts, organic bases, and their mixtures. A research paper titled "Polymer Additives Promoted Texturization on Monocrystalline Silicon for Solar Cell" from China’s Shaanxi University of Science and Technology nicely summarizes the developments in the field of additives. The paper highlights recent developments associated with the latest generation of additives using sodium lignosulfonate, sodium dodecyl sulfonate, cyclodextrin, and others as key functional chemicals.
According to Gerry Knoch, Managing Director, exateq, wafers – especially as cut – are usually of inconsistent quality and quite dirty, which leads to processing challenges. Residues on the wafers, combined with the saw-damage removal process, tend to cause foaming in the bath, disrupting uniform etching. While saw-damage removal traditionally did not require additives, their use has become standard over the past 2 to 3 years. Simply put, additives provide better process control.
RENA has created customized formulations such as MONOTEX H2.7 and H3.8, designed specifically for technologies like TOPCon and HJT. These additives not only improve pyramid uniformity and light trapping, but also help lower chemical consumption and enhance cleaning. Sharing more details about his presentation, "Wet Chemical Innovations in SHJ and TOPCon Cell Processing" at the TaiyangNews High Efficiency Solar Technologies 2024 Conference, Damian Brunner, Senior R&D Manager for Solar & Battery at RENA, emphasized that MONOTEX H2.7 optimizes texturing for TOPCon cells by improving Jsc while maintaining Voc and fill factor – resulting in efficiency gains of about 0.1% in Tier 1 high-efficiency production lines. The additive also supports better surface passivation and cleanliness, further boosting overall cell performance (see Wet-Chemical Processing In Solar Cell Manufacturing).
For HJT cells, RENA offers tailored texturing and pre-cleaning solutions. Its MONOTEX H3.8 additive helps achieve homogeneous pyramid coverage, a key factor for optimal passivation. Compared to competing solutions, this additive has shown improvements in fill factor and Jsc, which were validated in collaboration with CEA INES, according to Brunner.
The text is an edited excerpt from TaiyangNews’ latest Market Survey on Solar Cell Production Equipment 2025, which can be downloaded for free here.
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