A two-year tracing data of Daqing GW-scale comparison projects released by the SPIC (State Power Investment Corporation, a national authoritative center) indicates TOPCon outperforms its back contact counterparts by approximately 2%-3%. Another dataset from a major PV power station in the Shaanbei region showed TOPCon exceeding BC modules by over 5% in operational performance.
From a fundamental technological perspective, TOPCon established this advantage in large-scale ground-mounted power stations. It offers exceptional performance, high cost-effectiveness, strong scalability potential, and advanced technological compatibility.
Why have we recently observed TOPCon outperforming BC by more than 5 percentage points? How did this gap arise? First, the difference in bifaciality rates was around 10-15 percentage, which contributed approximately 1-1.5% in power generation gain. Secondly, its low-light effect contributed about 1% on average throughout the year. Combined, these two factors added up to around 2.5%.
Thirdly, it stems from technical adjustments to BC. The primary challenge with BC is addressing leakage current. By relocating the front grid lines to the rear and placing all metallization on the back, the PN junction becomes extremely close. To prevent hot spots caused by leakage, a metallization bridging technique was implemented. Its advantage is mitigating extreme scenarios—such as hot spots or breakdowns in BC due to leakage—but at the cost of introducing a uniform, minor leakage current. This technique resolves extreme issues, but it imposes a modest power generation penalty across all products.
The leakage effects and the quality, stability, and consistency of anti-leakage processes leads to overall performance, because within a single panel, even one cell with inadequate anti-leakage protection will drag down the entire panel's performance, aligning it with the lowest point—the so-called bucket principle. Similarly, this scales up to entire rows of panels, the entire array, and even megawatt- or gigawatt-scale projects. Thus, the larger the project, the more pronounced the differences become, and the longer the duration, the more evident they are.
Moving the front-side structure to the back-side creates significant crowding within the same area. Achieving proper insulation under these conditions poses a major challenge, increasing process complexity and particularly impacting yield rates. For instance, regarding reverse current metrics, under a -12V reverse voltage, BC's reverse current is around 1.5 amperes. It is considered a major risk because such a value would result in downgrading for TOPCon, yet it's accepted as a standard for BC.
TOPCon's overwhelming advantage is clear for utility-scale projects. While for rooftop distribution projects, the power gain contribution of TOPCon stems from two factors: the better low irradiation performance and 20 times less leakage current impact. If the roof is concrete and the modules are mounted on racks with a 0.5-meter clearance from the roof surface, the bifaciality-driven power gain of 0.8-1.0 percentage points results in extra yield gain.
