The solar industry entered 2026 carrying two compounding problems: a glut of manufacturing capacity that had hammered margins across the sector, and an efficiency ceiling that mainstream cell technologies could no longer push through. Both pressures pointed toward the same uncomfortable conclusion — incremental improvements were running out of room.
Then Trina Solar made an announcement. The company claimed it had crossed 28% efficiency on a large-format commercial cell — a number the industry hadn’t seen before at that scale.
A ceiling that mainstream solar couldn’t break
PERC cells dominated the industry for years, then TOPCon took over as the leading architecture. Both delivered meaningful efficiency gains in their time. But after multiple rounds of incremental upgrades, each technology has reached a point where further progress is marginal. The physics isn’t the only constraint — the economics are too.
Building an entirely new production line for next-generation technologies like HJT or full back-contact cells requires enormous capital investment. During a period of widespread overcapacity and compressed margins, that kind of spending is a hard sell. The industry needed a path forward that didn’t require tearing everything down and starting over. That context is what makes Trina Solar’s approach strategically significant — not just as a technical achievement, but as an industrial one.
What THBC actually is — and why the name matters
THBC stands for TOPCon-Compatible Hybrid Back-Contact Cell. The full name — TOPCon-compatible hybrid passivated back-contact cell — is deliberate. Every word carries weight.
The technology integrates TOPCon’s passivated contact, HJT’s amorphous-silicon passivation layer, and the front-side grid-free design that defines back-contact cells. None of these elements is new on its own. The novelty lies in how they’re combined.
Xie Zhigang, chief scientist at Trina Solar’s Central Research Institute, described the core breakthrough as bridging what have historically been two separate process ecosystems. PERC and TOPCon belong to high-temperature processing; HJT operates in low-temperature territory. These two routes have largely developed in parallel, rarely intersecting. THBC, Xie explained, achieves a “high-low temperature hybrid passivation” — fusing the superior passivated contact performance of TOPCon with the high-efficiency passivation capability of HJT, while adding a back-contact electrode structure.
This is also what distinguishes THBC from conventional TBC. Traditional TBC essentially relocates the front grid lines to the rear without changing the underlying architecture. THBC is a structural redesign, adopting an “intrinsic silicon + TCO” configuration that reduces rear parasitic absorption and improves passivation performance in ways a simple grid relocation can’t achieve.
The engineering problem THBC was built to solve
The limitations of conventional TBC are rooted in its reliance on single-step, high-temperature diffusion homojunction passivation. That process constrains hole extraction, leading to inadequate passivation and elevated contact resistance — two problems that put a hard ceiling on efficiency.
THBC addresses both directly. Instead of high-temperature boron diffusion, it uses low-temperature heterojunction deposition and a hole-selective emitter, producing superior surface passivation and a meaningful reduction in contact resistance. Durability was also a design consideration — through a selective enhancement approach, THBC optimizes vertical interface conductivity to improve long-term weatherability, a factor that matters as much for field reliability as it does for peak efficiency ratings.
The outcome: Trina Solar surpassed 28.0% efficiency on large-format 210R cells. According to the company, this is an industry first for that cell size.
Retrofitting, not rebuilding: the industrial strategy
The efficiency number matters. But for manufacturers weighing whether THBC is relevant to them, the production economics may matter more.
THBC is designed to be manufactured by retrofitting existing TOPCon lines. The additional equipment required is largely limited to PECVD and laser systems — targeted additions rather than wholesale replacement. Trina Solar estimates the capital expenditure at roughly one-quarter to one-third of what a dedicated HJT production line would require.
Zhang Yingbin, head of the New Product Technology Center at Trina Solar’s PV Product Business Division, put it plainly: the low-temperature process segment of THBC can fully utilize existing industry assets, production capabilities, and mature technological reserves. That framing matters — it means the transition path is incremental, not disruptive. Trina has already completed construction of a THBC pilot production line, with a gradual capacity ramp-up scheduled within the year.
Two technologies, two markets — and a note of caution
Trina Solar isn’t positioning THBC as a replacement for TOPCon. The two technologies are designed to serve different segments. TOPCon, with its strong bifacial performance, remains the preferred choice for ground-mount power plants where rear-side light absorption adds meaningful output. THBC, with zero front-surface shading, is optimized for mono-facial applications — primarily residential rooftop installations, with Europe and Australia as the initial target markets.
A separate dynamic is worth noting in the broader TBC landscape. Some competitors are pursuing aggressive cost-reduction strategies, including sharp cuts to silver paste consumption and early trials of copper paste substitution. These approaches lower manufacturing costs, but introduce uncertainties around long-term module reliability and power degradation that haven’t yet been validated at scale.
Whether THBC’s more conservative, retrofit-oriented approach proves more durable than those cost-cutting strategies remains to be seen. What’s clear is that Trina Solar is betting on efficiency and compatibility over short-term cost minimization — and the next few years of field data will be the real test of that wager.
Carlos is an engineer with strong expertise in technical and industrial topics. He previously worked at international companies such as Siemens and speaks Spanish, German, English, and Italian.
