TOPCon has firmly established itself as the mainstream technology in today’s PV production landscape. While the transition from PERC to TOPCon came with its own set of challenges, these have been progressively addressed through the concerted efforts of the solar industry, ranging from materials and equipment suppliers to cell and module manufacturers. This chapter outlines the most important technological advancements that have supported TOPCon’s rise, starting with developments at the wafer level, followed by innovations in processing that have enabled its rapid industrial adoption (see Wafers For High-Efficiency Solar Cells).

One of the key ingredients of most advanced cell architectures beyond PERC has been the change of wafer type, from p-type to n-type. Even within n-type, there are a few special requisites for every cell technology. The wafer quality requirements for TOPCon are somewhat in the middle of HJT and BC.

Electrical Parameters: The preferred resistivity for n-type wafers used in TOPCon is typically between 1 and 3 Ω cm, which provides a good balance between minimizing recombination losses and maintaining adequate conductivity. Carrier lifetime is another key parameter, with high-performance lines targeting bulk lifetimes above 1,000 µs, while it is even exceeding 2,000 µs in a few cases, aspiring for high Voc. The next item in the list is the oxygen content, which is generally kept below 10-12 ppm. Additionally, carbon content is also monitored, typically maintained below 1 ppm, as excessive carbon can lead to unwanted defect complexes during high-temperature processing. These electrical quality metrics collectively form the foundation for reliable and efficient TOPCon cell manufacturing.

Physical Parameters: While wafer thickness may come to mind first among the physical parameters, it is not the hot topic in the case of TOPCon. The average wafer thickness is between 125 µm and 140 µm, which is expected to go down to 110 µm in the next 5 years according to CPIA’s roadmap. What matters more for TOPCon is the dimensions of the wafer.

Rectangular Wafers: In recent years, wafer dimensions have again become a focal point in PV manufacturing. Now it is not about increasing the size, but rather moving away from the traditional square or pseudo-square to rectangular sizes. This is facilitated by the fact that every PV module is built on sliced silicon substrates. Thus, rather than cutting a wafer or cell into 2 equal parts, dividing them into asymmetrical pieces still enables them to meet the required module dimensions and corresponding power ratings for different applications. This also gives module makers the freedom to achieve the voltage and power requirements for a specific application by carefully selecting the size and count of cell strips.

Companies are also finding their own sweet spot for a wafer dimension. A few companies are even adopting more rectangular wafer dimensions than one to build modules for different applications. For example, Astronergy uses dimensions of 182 × 210 mm (commonly referred to as 210R) for its modules aimed at utility applications and 182.2 × 191.6 mm (191R) for DG application modules. JA Solar noted that at least 3 different wafer sizes are required to cater to the industry mainstream 54, 66, 72, and 78 cell module layouts. JA Solar tackled this issue smartly by using only one wafer size, i.e., 182 × 199 mm. The specialty of this wafer is that it can be cut in different ways to create modules of different sizes while maintaining the same width of 1,134 mm. For example, when the wafer is cut along the longer side, it can be used to create a 72-cell module with dimensions of 2,465 × 1,134 mm. When the same wafer is cut into 2 asymmetrical pieces of 105 mm and 94 mm, it can be used to create 66, 72, and 54 cell modules with dimensions of 2,382 × 1,134 mm, 2,333 × 1,134 mm, and 1,762 × 1,134 mm.

Quoting an internal market study report, Trinasolar shared insights into the global cell capacity and estimated production figures, focusing on wafer dimensions for 2023 and 2024 at the TaiyangNews High Efficiency Solar Technologies Conference. The study highlighted that the major rectangular cell dimensions are 210R, 191 × 182 mm (191R),and 199 × 182 mm (199R). By the end of 2023, global rectangular cell production capacity was expected to hit 84 GW, with 14.5 GW of it reflected in actual production. Looking ahead at that time, the capacity was projected to surge to 420 GW in 2024, accounting for over 80% of the cell market share. Rectangular cell production was expected to range between 200 GW and 300 GW in 2024. And as expected, most of the leading suppliers introduced modules based on rectangular wafers in 2024.

This text is an excerpt from the TaiyangNews Cell & Module Technology Trends 2025 report, which can be downloaded for free here.