Since 2024, the photovoltaic industry has largely moved beyond the roughly three-year debate over 182 and 210 wafer sizes. The 182x210 rectangular wafer has now become the industry standard, accepted by major manufacturers. The current focus has shifted to a competition among N-type TOPCon, heterojunction (HJT), and back-contact (BC) cell technologies. Essentially, this contest over cell technology is more meaningful than the previous size debate, as it drives technological progress and healthy industry development. Here, from a technical perspective, I attempt to discuss the competition among these three cell technologies in an objective manner.
First, N-type TOPCon has undoubtedly gained a leading edge, becoming the mainstream technology. It began large-scale production in 2022 and, by the end of 2024, accounts for around 70% of the market share, with most major companies opting for this route. TOPCon currently dominates in terms of maturity, cost, and reliability. In particular, the industry's adoption of laser-enhanced contact openings (LECO) last year has significantly boosted TOPCon efficiency, narrowing the gap with HJT. LECO also aids in the launch of single-glass products, further reducing material costs. Overall, it appears that TOPCon's mainstream status will remain unshaken for at least the next three years. However, predicting its dominance five years from now is challenging, as it's always difficult to forecast the solar industry that far out.
TOPCon faces two main issues: the difficulty of achieving further substantial efficiency improvements and the high energy consumption and carbon emissions resulting from its high-temperature processes. The Poly Finger process for partial front-side polysilicon passivation is challenging to scale for mass production.
Looking at HJT, this past year has been somewhat disappointing (actual shipments have fallen far below TOPCon's). TOPCon has nearly caught up in efficiency, HJT remains relatively expensive, and the cost-reduction advantage of thinner silicon wafers for HJT has diminished due to the rapid decline in silicon prices. HJT’s reliability also requires further optimization. Three key technologies—silver-plated copper, 0BB (busbar-free), and luminescent down-shifting encapsulation films—are essential for HJT's cost-reduction and efficiency improvement, but their integration for mass production and reliability validation will take time. HJT is a theoretically elegant technology with a simple process flow, high symmetry, and clear advantages in bifaciality and temperature coefficient, which translate into greater power generation gains. Efficiency improvements for HJT remain possible with copper plating, further optimization of microcrystalline processes, and better target materials. HJT’s most pressing challenge is to reduce costs while also improving product reliability. If HJT makes significant progress in these two areas within the next six months, it still has promising prospects.
Finally, regarding BC technology, I personally believe that BC is essentially a back-contact cell structure, which can be developed based on PERC, TOPCon, or HJT. BC cells have clear advantages. Since there are no front-side grid lines, BC cells naturally achieve higher front-side efficiency. Considering better front-side passivation, they can improve efficiency by 0.3%-0.5% over TOPCon. BC’s aesthetic appearance also makes it especially popular in distributed applications, such as residential rooftops. Additionally, each BC cell can achieve reverse bias (similar to bypass diode functionality), so in shaded conditions, BC modules theoretically deliver a 5-7% increase in generation.
However, BC cells also face major challenges. First, their specific process results in lower cell yields and higher costs. Second, the full-backside soldering in BC modules can cause cell warping, so BC cells must use thicker silicon wafers, though the impact of cell warping on long-term reliability still needs verification. The biggest challenge BC faces in ground-mounted power stations is its lower bifaciality due to its all-backside structure. Current BC modules have a bifaciality of less than 60%, even with 0BB technology, whereas TOPCon and HJT modules typically achieve around 80% and 85%, respectively. This bifaciality shortfall in BC limits its back-side generation, making it difficult to offset its front-side gains in the current levelized cost of electricity (LCOE) models used in power stations. Therefore, BC’s next major tasks are to reduce costs and improve bifaciality.
Regarding power generation performance among these three technologies, the key factors influencing module generation include temperature coefficient, low-light performance, bifaciality, operating temperature, and incident angle modifier (IAM) characteristics. HJT inherently excels in temperature coefficient, bifaciality, and low-light performance, so under comparable conditions without shading, mature HJT modules should slightly outperform TOPCon, with a 1-2% power generation advantage based on temperature and irradiance differences. BC cells, if based on TOPCon technology, should not differ significantly from traditional TOPCon in terms of temperature coefficient, low-light performance, and operating temperature. However, due to BC's lower bifaciality, it would not have an advantage in power generation without shading. The same conclusion applies to HJT-based HBC (heterojunction back-contact) when compared to traditional HJT. Nevertheless, under shaded conditions, BC modules' power generation advantage should be quite apparent.
An interesting topic for further industry research is the IAM performance of BC cells without front-side grid shading. Grid lines can create shadows at an angle, negatively affecting IAM performance, but they may also reflect some light back onto the module at an angle. It would be worthwhile to investigate which factor has a greater impact on IAM.
In summary, competition among these technologies is beneficial for the industry's progress. However, aggressive tactics between different routes are not constructive. The PV industry has moved past the protracted and somewhat dull size debate and returned to a technology-centered focus, which is a positive development. I hope to see more objective, science-based discussions backed by experimental data rather than mere market-driven arguments. As for which technology will ultimately prevail, it’s best left to time and market forces. In the end, technological progress remains the core driver of the PV industry, and more technological competition will only foster healthier industry growth.