Key takeaways:
According to LONGi, the BC architecture could maintain a projected 20-25 W module power advantage over TOPCon under comparable conditions
Testing data indicated lower hotspot temperatures for BC modules, which may influence long-term reliability in utility-scale installations
Modeled scenarios suggested that higher module power and improved degradation behavior translate into LCOE reductions compared to TOPCon
TOPCon technology is the current workhorse of the PV industry, with further room for development in terms of achieving peak efficiency, be it double-sided polysilicon deposition or achieving double-sided poly fingers. Ultimately, there would still be the possibility to increase the front-side power and overall efficiency as long as there is metallization on the front. Back contact (BC) technology seems to be the final step to reach maximum efficiency for a single-junction silicon solar cell.
TaiyangNews hosted a webinar titled ‘Unlocking the Utility Potential of BC Technology’ in H2 2025, where Alex Li from LONGi presented the company’s latest developments and why it positioned BC as the next step for utility-scale solar instead of pushing TOPCon.
According to Li, the main efficiency bottleneck in mainstream TOPCon is the high-temperature boron diffusion step on the front side, typically performed at 1,000°C, which introduces defects that limit voltage performance. Voc can be improved by replacing diffusion with passivating contacts using polysilicon and tunneling oxide layers. However, polysilicon introduces parasitic absorption, impacting the current. Therefore, the next improvement step is to use laser patterning to localize the polysilicon only under metal contacts. This adds to the complexity of the process and begins to resemble BC processing, which, if implemented, offers the advantage of eliminating metal shading on the front.
The elimination of front shading results in an optimized electrical and optical performance of the cell. This reasoning, he explained, is the basis for LONGi’s HPBC 2.0 architecture used in its Hi-MO 9 module.
In terms of the power roadmap, he compared projected power outputs between TOPCon and BC under similar technological improvements. Applying comparable advances, including improved metallization resistivity, advanced interconnection, and higher-lifetime wafers, BC modules are expected to maintain a 20-25 W advantage over TOPCon for modules of the same dimensions. For example, by the end of 2025, he indicated BC modules could reach around 660-670 W, while TOPCon modules would be closer to 640-650 W under comparable conditions. This projection is in line with what we have tracked at TaiyangNews in our TOP SOLAR MODULES feature (see TOP SOLAR MODULES Listing – December 2025).
He also emphasized hotspot behavior. Under standard test conditions of 1,000 W/m², shading a complete cell area in PERC or TOPCon modules can lead to hotspot temperatures of 160-170°C. In internal and third-party tests, BC modules showed significantly lower hotspot temperatures – around 114°C – under similar conditions. Under lower irradiance conditions (~550 W/m²), hotspot temperatures were reported to be about 160°C for PERC and TOPCon compared with roughly 43°C for BC. His argument was that while large utility plants may not experience regular shading from trees, partial shading from dust accumulation or bird droppings does occur between cleaning cycles throughout the 30-year operating lifetimes. Lower hotspot severity reduces long-term reliability risks.
Another point he addressed was bifaciality. Historically, BC modules were limited to rooftop applications given their near-zero bifaciality. He stated that improvements increased bifaciality to around 65% in 2024 and projected approximately 75% by the end of 2025, with potential to approach 80% in the future. Although this is lower than TOPCon’s typical ~85% bifaciality factor, he argued that total energy yield depends on absolute front-side power as well as bifacial response. He illustrated this using a simplified example of considering 85% bifaciality TOPCon module with 640 W power output versus a 75% bifaciality BC module with 670 W power. Assuming 1,000 W/m² front irradiance and 100 W/m² rear irradiance (10% albedo), the combined front-plus-rear output still favors BC by roughly 25 W due to higher front-side power. His conclusion was that absolute energy yield matters more than bifaciality percentage alone.
Linking these performance advantages to the levelized cost of electricity (LCOE), higher-power modules reduce the cost of balance-of-system (BoS) components, such as cables, trackers, combiner boxes, and inverters. Additionally, lower temperature coefficients and a projected linear degradation rate of about 0.35% per year improve lifetime energy yield. Combining these elements, based on modeled scenarios, Li presented examples suggesting LCOE reductions of approximately 3.8% and internal rate of return (IRR) improvements of around 5.3% over a 30-year project timeline with BC modules compared to TOPCon.