TOPCon requires 3 wet-chemical steps – texturing/cleaning, boron glass removal with junction isolation, and critical wraparound removal
HJT wet processing is similar but stricter with longer saw-damage etching and more emphasis on texturing
BC cells demand more complex wet processes especially in edge isolation, wraparound removal and rear surface polishing
Water and chemical savings are emerging as key factors, RENA’s phased Watersaving roadmap targets a 70% cut by 2030
The TOPCon cell manufacturing process involves 3 wet chemical steps, starting with texturing and cleaning. This stage removes saw damage while also conducting surface texturing and cleaning. Typically, the SDE and texturing processes are carried out in batch systems; however, SCHMID, a long-standing German supplier of wet benches, offers inline solutions.
The second stage involves the removal of boron glass and junction isolation in a 2-step batch process. After rear-side polysilicon passivation, wraparound removal becomes necessary, which is one of the most critical processes of TOPCon. In this process, the PSG or oxide layer is removed in a single-sided step, followed by batch wraparound removal and a final cleaning step before the wafers are screen printed.
According to Michael Vees, Sales Director Solar, RENA Technologies GmbH, the company’s key focus areas for TOPCon technology include enhancing the texturing process through its MONOTEX technology and introducing new additives to improve the cleaning process. By optimizing the etching formulation, these additives significantly enhance the selectivity and uniformity of the isolation step, reducing material losses and minimizing processing defects.
exateq focuses exclusively on HJT, where the process sequences differ only slightly from those of TOPCon. The main variations lie in process times – some require longer saw-damage etching, while others place greater emphasis on texturing. Cleaning approaches also vary: HJT manufacturers tend to be more meticulous, while TOPCon producers are generally not so aggressive and favor using ozone over hydrogen peroxide. Texturing methods have evolved as well. Both saw-damage etching and texturing now commonly use additives, a shift from earlier practices. As a result, many existing wet benches are being retrofitted to support these updated requirements.
Meanwhile, the industry is now also seriously evaluating BC, as are equipment makers. Back-contact (BC) is considered the ultimate cell architecture with the single-junction design, as the technology enables housing contacts of both polarities on the rear side of the cells. BC cells also differ from other technologies in their manufacturing processes, which is also true for wet-chemical treatment. While they share fundamental steps like cleaning, texturing, and etching with other technologies like TOPCon and HJT, BC cells typically require more processing stages. The etching and cleaning stages are especially critical due to the structure of the rear contacts. Edge isolation is more complex than in other cell types, as laser-doped areas must be protected, requiring precision in etching techniques. Additionally, wraparound removal and rear surface polishing demand carefully controlled chemical processes to maintain the integrity of the cell structure. Some manufacturers are even exploring ways to separate saw damage removal from texturing to further boost process efficiency.
SCHMID is promoting a combined system for texturing and polishing, which differs from standard TOPCon or PERC processes. According to Christian Buchner, vice president at SCHMID Group, typically, BC processing sequences start differently, often skipping saw damage etching. Instead, texturing comes in later stages. To meet industry demand, SCHMID developed a system that enables both single-side texturing and etching within a single tool. This approach was primarily introduced in China. However, due to industry restructuring and financial constraints, many manufacturers paused their pilot lines, delaying adoption, said Buchner, who expects manufacturers to resume adoption of this technology once market conditions improve (see Wet-Chemical Processing In Solar Cell Manufacturing).
Beyond cell technologies, water and waste management are also high on the agenda for RENA. At the TaiyangNews Solar Technology Conference, the company presented a stepwise outlook for reducing water usage in wet chemical process equipment. The company estimates that over the next 3 to 4 years, total water consumption in wet chemical processing could be reduced by more than 70% through a phased implementation of water-saving measures. The first level, called Watersaving 1.0, reduces water usage to 25% of the baseline of current mainstream production. This technology is currently in use. Watersaving 2.0, the second stage, is planned for release in 2026, targeting a further reduction to 50%. A subsequent stage, Watersaving 3.0, aims to decrease usage to 30%, leading to an overall water saving of 70% compared to conventional systems.
Buchner also highlighted that water consumption is an important area of development, particularly for Indian manufacturers. The shift toward sustainability has worked in SCHMID’s favor, according to Buchner, as the company’s wet-chemical processes reduce the water consumption by about 30% compared to the traditional batch processes. Water and chemical savings are increasingly becoming key considerations in equipment selection, according to Buchner.
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The text is an excerpt from TaiyangNews’ latest Market Survey on Solar Cell Production Equipment 2025, which can be downloaded for free here.