Two cell technologies compared on efficiency, temperature coefficient, degradation and bifaciality.
When buying solar panels you will meet two main cell technologies: PERC and TOPCon. At first glance the difference seems to be just a few percent of efficiency, but over a 25-30 year investment it becomes a significant difference in return.
What is PERC?
PERC (Passivated Emitter and Rear Cell) adds a passivation layer to the rear of a P-type silicon cell. It was the industry standard from 2018 to 2022. Cell efficiency is 22.5-23.5% and module efficiency 20.5-21.5%. As a mature technology its unit price is low.
What is TOPCon?
TOPCon (Tunnel Oxide Passivated Contact) adds a thin tunnel oxide and a doped polysilicon layer on N-type silicon. Cell efficiency reaches 25-26% and module efficiency 22-23%. N-type silicon largely eliminates the light-induced degradation (LID) seen in P-type.
Comparison
| Feature | PERC (P-type) | TOPCon (N-type) |
|---|---|---|
| Module efficiency | 20.5 – 21.5% | 22 – 23% |
| Temperature coefficient | −0.35 %/°C | −0.30 %/°C |
| First-year degradation | 2% | 1% |
| Annual degradation | 0.55% | 0.40% |
| Bifaciality | 70% | 80% |
| Year-30 performance | — | ≥ 87.4% |
What is the difference in real life?
A TOPCon system fitting on the same roof carries 8-10% more installed capacity than PERC. In hot regions where cell temperature reaches 65-70 °C in summer, the lower temperature coefficient raises this gain a little more. Dual-glass bifacial TOPCon modules can gain 10-25% extra energy from the rear.
Which one to choose?
- If roof area is limited: TOPCon; more kWp from the same area.
- Ground PV and MW scale: Bifacial TOPCon closes the price-per-Wp gap through balance-of-system (BOS) savings.
- If budget is limited and roof area is plentiful: PERC is an economical solution with low cost per Wp.
- If aesthetics matter: All-black TOPCon modules.
Temperature and low-light performance
At a sunny midday, cell temperature rises to 65-70 °C and power drops with each degree. TOPCon's −0.30 %/°C coefficient means about 2% less loss than PERC's −0.35 %/°C over a 40 °C temperature rise. Low-light performance in the morning, evening and on cloudy days is also better in N-type cells; this difference brings 1-2% extra annual energy.
Warranty and reliability
30-year product and performance warranties are becoming common in TOPCon modules. When looking at the price difference, evaluate total production (25-30 years) and warranty terms together.