Researchers from the German Aerospace Center (DLR) have conducted techno-economic analysis of producing n+-type polysilicon on oxide (POLO) back junction (BJ) solar cells in Germany and have concluded that the associated costs and benefits could be significant compared with photovoltaic cells manufactured using passivated emitter and rear cell (PERC) technology.
“We conducted the research in collaboration with the Institute for Solar Energy Research Hamelin (ISFH), Centrotherm and German technology company LPKF,” the research's lead author, Juan Camilo Gómez Trillos, told pv magazine. “We analyzed the production costs and minimum sustainable price of the emerging POLO BJ cells with n+-type passivating poly-Si on oxide (POLO) rear contacts, assuming its production under industrial conditions and analyzing from cell production costs down to electricity generation costs. The POLO BJ concept allows higher efficiencies for photovoltaic cells compared to concepts without passivating contacts. In addition, the POLO BJ concept has certain advantages compared to the cell concepts in the market, such as lower silver consumption allowing lower production costs, or leaner process flow.”
The scientists explained that, although PERC has largely been replaced by tunnel oxide passivated contact (TOPCon) technology, the POLO BJ concept offers advantages over TOPCon. These include the use of aluminum-based metallization instead of high amounts of silver and a shift toward all-back-contact designs. “The value of next-generation solar cell concepts should not be assessed solely in terms of efficiency, but also in terms of manufacturability and system impact,” said Gómez Trillos. “POLO BJ shows potential as a high-efficiency technology with tangible economic benefits across the value chain.”
In the study “The Cost of Ownership and Minimum Sustainable Price of POLO BJ Cells Produced in Germany,” published in Advanced Energy & Sustainability Research, the research team explained that POLO BJ cells may be easily produced with existing and slightly adapted PERC production lines, with only one additional laser step being required.
The manufacturing process begins with a cleaned p-type silicon wafer, followed by the formation of a thin silicon dioxide (SiO₂) layer on both sides. A heavily doped n⁺ polysilicon layer is then deposited using low-pressure chemical vapor deposition (LPCVD) and subsequently thermally oxidized. The front-side silicon dioxide layer is selectively removed using either wet chemical processing or laser ablation, while the rear side remains protected during the texturing step. Passivation layers are applied using plasma-enhanced chemical vapor deposition (PECVD), and the process is completed with laser contact opening and screen printing to form the electrical contacts of the solar cell.
For their modeling, the academics assumed a production capacity of 5 GW and noted that, at this scale, a single plant could supply roughly 30% of Germany’s 2024 photovoltaic demand of 16.2 GW. A baseline POLO BJ cell efficiency of 24.2% was assumed, based on demonstrated industrial performance in M2-format devices, with a maximum scenario of 25% considered for sensitivity analysis. Plant output was evaluated under constant annual cell throughput, meaning higher efficiencies directly increase total peak power capacity. For comparison, PERC technology was modeled under identical conditions, including the same wafer format and plant size, but with a maximum efficiency of 23.1%.
Cost analysis was performed using a bottom-up cost of ownership model based on the guidelines of the Semiconductor Equipment and Materials International (SEMI) association and Germany's mechanical engineering association VDMA. The model incorporated production tool costs, throughput, materials, and energy use. Minimum sustainable price was calculated to translate production costs into market-relevant pricing, including capex, opex, taxes, working capital, depreciation, and a weighted average cost of capital of 8%. Finally, levelized cost of electricity (LCOE) was estimated for utility-scale systems using POLO BJ and PERC modules.
The analysis showed that total investment costs differ moderately between the two cell concepts, ranging from $171.0 million for PERC to between $177.5 million and $182.1 million for POLO BJ. The main cost driver is the higher tool requirement for POLO BJ processes. When net working capital is included, total investments rise significantly, with POLO BJ-L becoming the most cost-efficient option. Variable and operational costs were also lowest for POLO BJ, with the main cost contributors being wafers and process materials, followed by labor and utility bills. Higher PERC costs, meanwhile, were found to be driven by its lower efficiency and higher cell demand.
Cost of ownership (CoO) analysis also showed clear advantages for POLO BJ concepts, with values of $0.0579–0.598/W compared to $0.0631/W for PERC. The minimum sustainable price (MSP) followed a similar pattern, with POLO BJ-L achieving the lowest value of $0.0716/W, while PERC reached $0.0775/W. Additional financial components such as taxes, capital costs, and operating expenses contribute significantly but do not change the relative ranking. Overall, POLO BJ became economically superior to PERC above certain efficiency thresholds. Finally, levelized cost of electricity (LCOE) analysis showed that POLO BJ-based systems reduce electricity costs compared to PERC in both Germany and Spain.
“The higher efficiency translates to lower LCOE at system level, which varies regionally,” said Gómez Trillos. “Under Southern European conditions, values of $0.0332/kWh were obtained for monofacial glass–backsheet modules and $0.0302/kWh for bifacial glass–glass modules. Furthermore, several aspects can influence the production costs and the minimum sustainable price of the photovoltaic cells. Local factors, such as electricity prices, labour costs, logistic costs, local corporate income taxes, or capital costs, can to a certain extent affect production costs at different locations. According to our analysis, only the labour and electricity costs would have together a share of 23% of the minimum sustainable price of POLO BJ cells in Germany. These factors can considerably fluctuate from country to country, leading to lower or higher results depending on the location.”
The researchers are convinced that POLO BJ cells represent a potential candidate for local production of PV cells in Europe. “During the project, we did not work on a concrete time frame for a potential implementation, but we are aware of projects dealing with the transfer of the knowledge on POLO technologies to the industry, which might result in concrete implementation in the following years,” Gómez Trillos concluded.
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