Why TOPCon Beat HJT: Path Dependence Explains the Solar Cell Technology Race
Introduction
In 2023, many solar cell manufacturers faced the same boardroom question: if the industry must move from P-type PERC to N-type technology, should the next investment go to TOPCon or HJT?
On paper, HJT looked elegant. It had strong passivation, low-temperature processing, excellent bifacial performance, and a promising theoretical ceiling. But in real factories, the decision was often made by one number: the cost of conversion.
For a company already running PERC lines, upgrading to TOPCon could cost roughly RMB 50-80 million per GW. Building a new HJT line often required RMB 200-350 million per GW, even though equipment prices have been falling. That difference was too large to ignore.
So TOPCon did not win simply because it was the most advanced technology. It won because the road from PERC naturally led to TOPCon.
The core idea
The solar industry did not choose TOPCon in a vacuum. It chose TOPCon under the weight of ten years of PERC equipment, PERC engineers, PERC suppliers, PERC quality data, and PERC production habits. This is a textbook case of path dependence.
Technical Parameters
Market and technology comparison
| Item | TOPCon | HJT | BC |
|---|---|---|---|
| Main industrial position | Dominant N-type route | High-potential challenger | Premium and third-route contender |
| 2025 estimated module output share | About 77.1% globally | Much smaller share | Smaller but growing |
| 2025 estimated cell shipment | About 320GW | About 48GW | About 36GW |
| Mass production efficiency | Around 25.5-26.5% | Above 27% in leading lines | Depends on route, strong premium potential |
| Typical PERC compatibility | High | Low | Medium to low, depending on TBC or HBC design |
| Upgrade cost from PERC | About RMB 50-80 million/GW | Usually new line required | Higher than TOPCon, complex process |
| New equipment investment pressure | Lower for existing PERC players | High | High to medium-high |
| Key process difficulty | Boron diffusion, passivated contact, metallization | Low-temperature thin film, TCO, low-temperature paste | Patterning, laser opening, masking, alignment |
| Main advantage | Fast industrial scale-up | Better structure for tandem potential | No front grid, lower optical loss, premium appearance |
| Main weakness | Efficiency improvement is slowing | Weak legacy compatibility | Process complexity and yield challenge |
Why the cost gap mattered
| Dimension | TOPCon | HJT |
|---|---|---|
| Switching cost | Low: partial PERC line upgrade | Very high: largely new production line |
| Equipment continuity | Many PERC tools and factory practices can be reused | Equipment system is substantially different |
| Talent base | PERC engineers can adapt faster | Requires new thin-film and low-temperature process thinking |
| Supply chain | Quickly inherited and expanded from PERC ecosystem | Needs separate paste, target, TCO, and process ecosystem |
| Yield ramp-up | Easier for PERC-based manufacturers | Higher learning cost and higher ramp-up risk |
Technical Advantages
Path dependence: the hidden force behind TOPCon's victory
Path dependence means that today’s decision is heavily shaped by yesterday’s investment. Once an industry has built equipment, trained people, written standards, accumulated failure data, and optimized supply chains around one route, it becomes expensive and risky to jump to another.
TOPCon received all three layers of path dependence from PERC.
Lower switching cost: TOPCon only required several major new process modules on top of existing PERC lines, such as boron diffusion and LPCVD or PECVD passivated contact steps.
Positive feedback loop: More TOPCon lines encouraged equipment makers, paste suppliers, process engineers, and quality teams to improve TOPCon faster.
Lock-in effect: Once TOPCon became the mainstream language of production, talent, standards, troubleshooting, and supplier development all started flowing in the same direction.
TOPCon became stronger because more factories chose it. More factories chose it because it became stronger. That loop was decisive.
Why HJT lost the industrial race, not the technology race
HJT did not lose because it was a poor technology. In many ways, it is technically attractive.
Symmetrical structure supports strong bifacial performance.
Intrinsic amorphous silicon provides excellent passivation.
Low-temperature processing can reduce thermal stress.
Lower temperature coefficient helps performance in hot climates.
HJT has strong compatibility with future perovskite tandem cells.
But HJT had a serious industrial problem: it did not inherit the PERC production base.
A factory choosing HJT had to consider replacing large parts of existing assets, retraining engineers, building a new supplier system, accepting a new yield ramp-up cycle, and taking greater investment risk. In a period when solar manufacturing margins were under pressure, this was not just a technology decision. It was a survival decision.
BC: the third route, but not an easy shortcut
BC technology is often described as another possible winner, but its path is different from both TOPCon and HJT.
BC cannot fully inherit the traditional PERC structure because back-contact architecture changes the cell design fundamentally. It needs patterning, laser opening, masking, and precise back-side contact formation. That makes it much more complex than TOPCon.
However, BC can attach itself to different base technologies:
TBC: TOPCon plus back contact, sharing some TOPCon process and equipment logic.
HBC: HJT plus back contact, combining HJT passivation with back-contact structure.
BC is not simply a crossroads. It is more like a new highway that can carry different types of vehicles. But the highway itself still has to be built, and that is expensive.
The key problem is yield. Every extra process step can become a yield killer. Until BC can bring yield, cost, and throughput close to TOPCon levels, it will remain strong in premium markets but difficult to replace TOPCon at massive scale.
Product Applications
What this means for solar manufacturers
For manufacturers planning new cell or module capacity, the TOPCon-HJT-BC debate is not only about cell efficiency. It is about factory economics.
Existing PERC-based producers naturally moved toward TOPCon because the upgrade route was clearer.
New entrants with enough capital may consider HJT or BC, but they must accept higher process risk.
Premium module makers may use BC to target distributed generation, rooftop aesthetics, and high-efficiency segments.
Long-term technology investors are watching HJT-perovskite and TOPCon-perovskite tandem routes closely.
What this means for production engineers
For front-line engineers, the next three years are likely to remain TOPCon-heavy. The most valuable practical skills will still be related to full-process TOPCon control.
Important areas include:
Pre-cleaning and surface preparation
Boron diffusion control
BSG removal
LPCVD or PECVD passivated contact formation
Annealing process windows
Al₂O₃ and SiNₓ film deposition
Metallization and paste matching
Failure analysis and yield improvement
At the same time, engineers should not ignore perovskite tandem progress. The key indicators to watch are not only lab efficiency, but also stability, large-area performance, and process repeatability.
The perovskite tandem turning point
Path dependence is powerful, but it is not permanent. It can break when the performance gain of a new route becomes large enough to justify the switching cost.
This is why perovskite tandem matters. If tandem technology reaches stable industrial production, the old debate between single-junction TOPCon and single-junction HJT may become less important. The industry may shift from optimizing crystalline silicon alone to rebuilding the whole efficiency ceiling.
HJT supporters are betting heavily on this. HJT’s low-temperature process and symmetrical structure make it naturally suitable for perovskite tandem integration. But TOPCon companies are also developing tandem solutions, so HJT is not the only possible winner.
Contact and Purchase
Three clear judgments
First, TOPCon will remain the mainstream route in the next three years. From 2026 to 2029, TOPCon is likely to keep more than 70% market share. Its advantage is not only efficiency. It is equipment availability, trained engineers, supplier maturity, quality databases, and lower upgrade risk.
Second, HJT needs perovskite tandem to create a real comeback. If HJT remains only a single-junction technology, it will struggle to reverse TOPCon’s industrial scale. If perovskite-HJT tandem reaches stable mass production, the story may change.
Third, BC is TOPCon’s strongest structural threat if it solves yield and cost. BC has visible advantages in appearance and optical loss reduction, especially for high-end rooftop and distributed applications. But unless the process becomes stable and affordable, it will stay as a premium route rather than a universal replacement.
Final thought
The best technology does not always win first. The technology that fits the existing road often wins faster.
TOPCon beat HJT not because HJT lacked potential, but because PERC’s decade-long industrial accumulation pointed directly toward TOPCon. Equipment, engineers, suppliers, process windows, and factory habits all pushed in the same direction.
HJT now needs a large enough technology dividend to pull the industry away from its historical path. BC is trying to build its own path through heavy investment and process maturity. Perovskite tandem may become the next real turning point.
Ooitech's View
As an equipment-side observer, Ooitech sees TOPCon’s rise as a reminder that solar technology transitions are decided on the production floor, not only in efficiency charts. For module manufacturers, the winning route must match equipment continuity, yield ramp-up speed, material availability, and operator learning curves. The next disruption will likely come only when tandem technology offers a performance jump large enough to overcome today’s TOPCon lock-in.
