Monocrystalline vs polycrystalline
Solar cells are made from silicon wafers. Monocrystalline wafers are cut from a single grown crystal, which gives a uniform dark look and higher efficiency. Polycrystalline wafers are cast from many crystals: cheaper to make, speckled blue, and less efficient. For homes, monocrystalline has taken over, so the useful question today is which kind of monocrystalline cell a panel uses.
The cell technologies you will see
PERC (p-type)
Passivated Emitter and Rear Cell was the mainstream design for years. It is still sold, often at lower prices, but most manufacturers are moving their premium ranges to n-type cells, which tend to degrade more slowly.
TOPCon (n-type)
Tunnel Oxide Passivated Contact cells are the current mainstream for new panels. They improve on PERC’s efficiency and long-term output using a manufacturing process close to existing PERC lines, which is why they arrived quickly and widely.
Heterojunction, HJT (n-type)
Heterojunction cells combine crystalline silicon with thin amorphous silicon layers. Their strength is heat performance and low degradation. The REC Alpha Pure-RX (450–470W) is an example: its datasheet gives a temperature coefficient of −0.24%/°C and promises 92% at year 25.
Back-contact: ABC and HPBC (n-type)
Back-contact cells move all the electrical contacts to the rear, so no silver lines shade the front. That raises efficiency and gives a clean look. The AIKO Neostar 2P (500–525W, 60-cell) (all-back-contact) lists efficiency of 22.6% to 23.7% across the range; LONGi’s Hi-MO X10 (back-contact) uses LONGi’s hybrid passivated back-contact design and comes with a 30-year linear power warranty.
Tandem (perovskite on silicon)
Tandem cells layer a perovskite cell on top of a silicon cell to capture more of the spectrum. Oxford PV announced a 26.9%-efficient residential-size module in 2024. It is a technology to watch, but we found no UK retail route for it when we checked on 15 October 2026.
At a glance
| Cell type | Where it sits | Typical strengths | Worth asking |
|---|---|---|---|
| PERC (p-type) | Older mainstream | Lower price | Degradation rate and power warranty length |
| TOPCon (n-type) | Current mainstream | Good efficiency for the price | Exact variant efficiency |
| Heterojunction | Premium | Heat performance, low degradation | Temperature coefficient |
| Back-contact (ABC, HPBC) | Premium | Highest efficiency, clean front | Price per watt vs. the roof space you have |
Appearance options
All-black panels look uniform on dark roofs. In-roof systems sit flush with the tiles. Solar slates and roof tiles replace roof covering altogether, and that is where most British-made products sit: see solar roof tiles and slates and British-made solar panels. For the numbers to compare between any of these, use best solar panels UK.