What Comes After TOPCon? Back-Contact and Perovskite Panels Explained
Back-contact panels are already the answer to “what’s next after TOPCon.” Perovskite-silicon tandem panels are the answer after that, and unlike back-contact, you can’t buy one for your roof yet.
What’s already replacing TOPCon
TOPCon became the default panel technology on UK quotes by pushing efficiency past PERC without needing new factories to make it. The step above it works the same way: LONGi’s HPBC and Aiko’s ABC panels use the same kind of N-type silicon wafer as TOPCon, they just move the wiring grid from the front of the cell to the back. That clears the front surface for more light and gets rid of the visible grid lines, which is why these panels get marketed on looks as much as output. LONGi’s Hi-MO X10 runs its HPBC 2.0 cells at roughly 23 to 24% module efficiency, and Aiko’s ABC panels sit close behind at around 24 to 25%. Both are sold to UK installers now, priced above standard TOPCon.
How the cell technologies actually compare
| Technology | Typical module efficiency | Available in the UK now? | Where it sits on price |
|---|---|---|---|
| PERC | 20.5-21.5% | Yes, budget tier | Cheapest |
| TOPCon | 21-24% | Yes, the current default | Mid-range |
| Back-contact (HPBC, ABC) | 23-25% | Yes, premium tier | Above TOPCon |
| Heterojunction (HJT) | 22-23% | Yes, premium tier | Above TOPCon |
| Perovskite-silicon tandem | 24-29% commercial, 35.5% lab record | No, not with a standard warranty | Unknown; not priced for residential yet |
PERC still wins on upfront cost, which is why it hasn’t disappeared from budget quotes. TOPCon has the widest track record of installers and warranties behind it, and that counts for more than a percentage point of efficiency on something you’re buying for 25 years. Back-contact and HJT win on output and, for back-contact, on how the panel looks on a roof. Perovskite tandems only win on paper right now: a genuinely higher ceiling with none of the field history that makes a 25-year warranty worth trusting.
Why back-contact panels look different on a roof
A standard panel has a visible grid of thin silver wiring across the front of every cell, carrying the current away. Back-contact panels move that entire grid to the rear, so the front is a plain, unbroken black surface. It’s a genuine aesthetic difference homeowners notice, not just a spec sheet number, and it’s a big part of why these panels get sold at a premium rather than purely on the efficiency gain.
Why perovskite tandems aren’t on a quote yet
A perovskite-silicon tandem stacks a perovskite layer on top of a standard silicon cell, so it catches a wider slice of the light spectrum than either layer could alone. LONGi announced a certified 35.5% efficiency record for this combination in July 2026, verified by the European Solar Test Installation. That’s a real number, but it’s a lab cell, not a panel. Commercial modules from companies actually shipping the technology, like Oxford PV, have been closer to 24.5% efficiency, and even that batch went to US utility-scale customers in 2024 rather than UK homes. Perovskite also degrades differently to silicon, and a 25-year warranty depends on years of field data nobody has yet. Industry estimates put full-size, fully warrantied residential panels somewhere around 2028 to 2030. Worth knowing the technology exists, not worth waiting for.
Does any of this change what you should quote for now
Not much, for most roofs. TOPCon remains the panel most UK installers default to, and it’s a mature, well-warrantied choice. Back-contact and HJT are worth asking about if you want the highest output per panel or a cleaner look and don’t mind paying for it, particularly on a smaller roof where every extra percentage point of efficiency does more work. Perovskite tandems are worth knowing about so a “revolutionary new panel” pitch doesn’t catch you off guard, but there’s nothing to actually buy yet. Our panel and battery comparison tool covers the models you’ll actually see on a 2026 quote, including two back-contact and HJT options, side by side.
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Frequently asked questions
What solar panel technology is replacing TOPCon?
Back-contact panels, sold as LONGi's HPBC and Aiko's ABC, are already on the market as the step up from TOPCon. They're built on the same kind of silicon wafer, just with the wiring moved to the rear of the cell, and they're sold now as a premium tier above standard TOPCon.
Are back-contact solar panels the same as TOPCon?
No, though they're related. TOPCon adds a passivating layer to the back of the cell to cut energy loss. Back-contact goes further and moves the entire wiring grid to the rear too, clearing the front surface completely. LONGi's HPBC 2.0 actually combines both approaches on an N-type wafer.
Can I buy a perovskite solar panel yet?
A full residential warranty isn't there yet. LONGi certified a 35.5% lab efficiency record for a perovskite-silicon tandem cell in July 2026, but that's a lab result, not a product. Industry estimates put installer-grade panels with a standard 25-year warranty somewhere around 2028 to 2030.
Are back-contact solar panels worth the extra cost?
It depends what you're weighing it against. Back-contact panels cost more than TOPCon and typically run a percentage point or two higher on efficiency, plus a plain black front with no visible grid lines. If your roof already has enough space for a standard TOPCon array, the extra cost buys looks and a small output gain rather than a system that wouldn't otherwise fit.