You’ve carefully selected high-efficiency TOPCon cells for your new bifacial module design, confident you’ve got the core component right. But what about the rest of the Bill of Materials (BOM)—like the backsheet? A transparent one is the standard choice, right? It’s a logical assumption; you want light to pass through to the rear side of the cells.
But what if that logical choice is leaving significant performance gains on the table? What if a simple switch in your backsheet material could boost your module’s rear-side power capture by over 8%?
This isn’t just a theory. It’s a measurable reality that highlights a critical shift in how we should think about module components. They aren’t just passive parts—they form an active optical system. And optimizing that system is key to unlocking the full potential of bifacial technology.
Why Rear-Side Optics Matter More Than Ever
Bifacial solar modules are remarkable because they capture light from both sides. The front side works like a traditional module by capturing direct sunlight, while the rear side captures reflected light (albedo) from the ground or mounting surface. The extra energy generated by the rear side is called bifacial gain.
With the rise of n-type TOPCon (Tunnel Oxide Passivated Contact) cells, which have a naturally high bifaciality of over 80%, maximizing this gain is no longer a minor tweak—it’s a major value driver.
The problem is, simply letting light pass through a transparent backsheet isn’t the most efficient way to illuminate the rear of the cells. A significant portion of the light entering from the back can pass straight through the gaps between cells, escaping without ever generating a single electron.
Your choice of backsheet and encapsulant, then, becomes a crucial piece of optical engineering.
The Experiment: Transparent vs. Patterned Backsheets
We know that patterned, or structured, backsheets are designed to scatter light instead of just letting it pass through. This redirects photons that would otherwise escape, bouncing them back onto the active rear surface of the solar cells.
But does it work? And can you take it too far? To find out, we put it to the test.
On our full-scale R&D production line at PVTestLab, we manufactured three sets of identical glass-backsheet TOPCon modules. The only variables were the backsheet and encapsulant combinations. Their performance was then measured with our AAA Class flasher to get precise, comparable data.
Here’s what we tested:
- The Control: A standard transparent backsheet with a transparent encapsulant.
- The Challenger: A white patterned backsheet with a transparent encapsulant.
- The Combination: A white patterned backsheet with a patterned encapsulant.
The results were fascinating and revealed a clear winner.
Finding #1: The Patterned Backsheet is a Clear Winner
Our baseline module with the fully transparent setup achieved a respectable bifaciality factor of 10.37%. This is a solid, industry-standard result.
Swapping the transparent backsheet for a white patterned one, however, pushed the bifaciality factor up to 11.23%.
That might seem like a small number, but it represents a relative increase of 8.3% in rear-side power gain. Over the 25-year life of a solar installation, that adds up to a significant amount of extra energy and revenue, all from a single component change. This test confirms that a patterned backsheet effectively scatters light back onto the cells, converting would-be-wasted photons into measurable power.
Finding #2: The Surprising Twist—More Isn’t Always Better
Instinct might suggest that if one patterned layer is good, two must be better. So, we tested a third configuration: the winning patterned backsheet combined with a patterned encapsulant.
The result? The bifaciality factor dropped to 10.82%.
While still better than the fully transparent baseline, it was a noticeable step down from the patterned backsheet alone. It’s a perfect illustration of a critical principle in module design: components don’t work in isolation. The interaction between the two patterned surfaces may have created an inefficient scattering effect, preventing light from being optimally redirected to the cells.
„The best materials can underperform if the system isn’t optimized,“ notes Patrick Thoma, PV Process Specialist at PVTestLab. „This is why we test the complete package. The data showed us that the synergy between the patterned backsheet and a clear encapsulant delivered the highest measurable gain.“
Key Takeaways for Your Next Module Design
This experiment reveals a few powerful, actionable insights for anyone developing or manufacturing bifacial modules.
- Your Backsheet is an Active Optical Component: Stop thinking of your backsheet as just a protective layer. For bifacial modules, it’s a key part of the optical system. Choosing the right one directly increases your module’s energy yield.
- A Patterned Backsheet is a Powerful Upgrade: For TOPCon modules, using a white patterned backsheet is one of the most effective ways to maximize bifacial gain by improving internal light scattering.
- Test the Entire System: The best component on paper might not be the best for your specific BOM. The only way to know for sure how materials will interact is to build and test new solar module concepts in a controlled, industrial environment. Conducting structured experiments on encapsulants and backsheets is essential to validate performance before committing to mass production.
The path to higher efficiency and better performance is paved with data. By questioning assumptions and testing every variable, we can uncover hidden gains that push the entire industry forward.
Frequently Asked Questions (FAQ)
What is a „bifaciality factor“?
The bifaciality factor is a percentage that represents how efficient the rear side of a solar cell is compared to its front side. It’s calculated by dividing the maximum power generated from the rear side by the maximum power from the front side, measured under standard test conditions. A higher factor means more effective rear-side power generation.
Does a white patterned backsheet reduce the temperature of the module?
Yes, a white backsheet generally reflects more light and absorbs less thermal energy than a fully transparent one, which can contribute to a lower module operating temperature (NOCT). A cooler module operates more efficiently, providing a small additional performance benefit on top of the optical gain.
Is this result specific to TOPCon cells?
While this test was conducted with TOPCon cells, the optical principle of scattering light to increase capture applies to other bifacial technologies like PERC and HJT. However, the exact percentage of gain will vary based on the cell’s specific characteristics and the module’s overall design. Validation for your specific cell type is always recommended.
How does a patterned backsheet impact manufacturing and lamination?
Incorporating a patterned backsheet requires no significant changes to a standard lamination recipe. It can be treated just like a conventional backsheet, making it a low-friction, high-impact upgrade for manufacturers looking to boost bifacial performance.
Ready to Optimize Your Module?
Choosing the right materials is the first step, but the next is to validate that they work together to deliver the results you expect. If you’re exploring how to optimize your own bifacial module design, understanding how all the pieces interact is key.
Have questions about your specific Bill of Materials? Consult with our process specialists to uncover the hidden gains in your module design.