Advances in solar panel technology have been partially driven by enhancements to the materials and architectural designs of earlier models. TOPCon solar panel technology is developed based on the widely used PERC technology today and aims to address major limitations of PERC panels and push the boundaries of solar panel efficiency.
Below, we'll explore the key facets of this technology and help you make a wise investment in solar panels.
Table of Contents
What Is the TOPCon Solar Panel Technology?
The concept and development of TOPCon (Tunnel Oxide Passivated Contact) technology can largely be led by researchers at Fraunhofer ISE.
A 2014 paper by the Fraunhofer ISE team first detailed the design and performance improvements of solar panels using the TOPCon technology.
Composition & Structure (vs. PERC)
As an ancestor of TOPCon, the PERC technology was introduced for the first time with the adoption of a rear passivation layer to reduce recombination on the rear side.
Comparatively, the TOPCon technology achieves passivation in a moderately different manner.
In a TOPCon solar cell, a super-thin (only a few nanometers) layer of silicon dioxide (SiO₂) constitutes the tunnel oxide layer, which blocks certain charge carriers while allowing electrons (in the context of an n-type cell) to ‘tunnel’ through quantum mechanically.
The cell also applies a layer of doped polycrystalline silicon on top of the tunnel oxide layer. This doped layer is typically phosphorus-doped and serves to improve electrical conductivity and reduce transmission losses.
Here's an overview of the different layers of a TOPCon solar cell, which can also be referred to in the figure below.
- Front Contact
- Anti-Reflective Coating (ARC)
- Front Passivation Layer: Though can sometimes overlap in function with the ARC, the front passivation layer is specifically aimed at reducing surface recombination.
- Absorption Layer: While the base sublayer can be either n-type or p-type, the n-type material is frequently utilized in modern products as it provides some impressive advantages. In an n-type cell, the emitter sublayer is usually p-type. Together, they create a p-n junction to facilitate charge separation.
- Tunnel Oxide Layer
- Polycrystalline Silicon Layer
- Rear Contact
How a TOPCon Solar Cell Works?
Like many other cell technologies, the working process of a TOPCon cell begins with light absorption, where sunlight strikes the ARC layer on the surface, which minimizes reflection, allowing more photons to enter the cell.
These photons excite the electrons, and set off generation and separation of electron-hole pairs in the absorption layer. The combination of the tunnel oxide and polycrystalline silicon layers provides advanced passivation, which implements accurate carrier selection allowing a certain type of charge carriers to pass through easily while blocking the other.
This design further ensures that more favorable charge carriers are collected and fewer are lost, significantly enhancing the cell's efficiency.
Finally, the electrical current generated by the separated charge carriers is collected and transported through the front and rear contacts.
TOPCon vs. Other High-Efficiency Panel Technologies
As a young technology, comparing it with other high-efficiency panel techs is beneficial for both manufacturers and customers.
TOPCon vs. PERC Panels
The history of PERC technology can be traced back to the 1980s. After over three decades of development, it has become a widely adopted architecture to enhance panel passivation, reduce recombination and improve efficiency.
Building on the principles of PERC, TOPCon provides an upgraded passivation solution. Though the production cost could be still higher, its enticing compatibility with PERC production lines and higher efficiency render it accepted as a next-generation mainstream efficient solar cell in a short time.
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- PERC Solar Panel: Strengths, How It Works, vs. Other Panel Techs
TOPCon vs. HJT Panels
HJT technology is an ‘integrator’ as it combines the use of passivation techniques as well as modifications on the absorption layer to reap higher efficiencies.
To be more specific, this technology innovatively combines crystalline silicon (c-Si) with amorphous silicon (a-Si) thin-film layers to create a hybrid cell. The a-Si material not only contributes to passivating the surface but also offering higher absorption coefficient in particular parts of the light spectrum, complementing the absorption capability of c-Si material.
Thanks to the flexibility in their architecture, HJT panels are generally designed as bifacial modules to further increase energy yield.
The major drawback of HJT panels is their more complex manufacturing process and resulting higher cost. In contrast, the ability to be integrated into existing PERC production lines with minimal changes makes TOPCon panels more cost-effective, shaping them a great, high-efficiency panel option for projects of all sizes.
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TOPCon vs. IBC Panels
IBC panels represent another route to obtain higher efficiencies.
The core feature of IBC solar panels is the relocation of front contacts to the rear side for the sake of maximum area available for sunlight absorption. Coupled with the integration of passivation techniques, IBC panels are also a popular high-end panel product.
On the other hand, the eliminated need for front-side metal contacts in IBC panels leads to a sleek, all-black look, making them a good fit for projects where visual appeal is highlighted.
However, IBC technology also requires a more complex manufacturing process and cannot be simply implemented by modifying existing facilities like the TOPCon technology. This factor causes IBC panels to be generally more expensive than TOPCon products.
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- IBC Solar Panel Explained + Strengths and vs. Other Techs
What Makes TOPCon Solar Modules Competitive?
In a nutshell, several key advantages of TOPCon solar modules let them emerge as a competitive technology in the solar industry.
- High Efficiency & Output: By leveraging the benefits of the n-type base and integration of a thin, tunneling oxide layer and a highly doped polysilicon layer on the rear side, TOPCon solar modules effectively reduce recombination losses and provide higher efficiency, which can reach around 25%.
- Excellent Real-World Performance: The superior wafer and other materials utilized in TOPCon panels deliver a low temperature coefficient and enhanced low-light performance. This makes sure these panels present robust results under varying environmental conditions.
- Durability & Longevity: Modern TOPCon panels are less prone to degradation caused by boron-oxygen defects, leading to lower degradation rates and longer lifespan and ultimately improved long-term energy yields.
- Cost-Effective Investment: For both manufacturers and buyers, investing in TOPCon solar panels can bring in a good ROI. The adaptability of TOPCon technology makes it easier for manufacturers to adopt it and scale production. The mitigated production risk and cost afterward enable TOPCon panels and a cost-effective option for customers.
Can TOPCon Solar Panels Be Bifacial?
Yes, TOPCon solar panels can indeed be configured as bifacial modules as other advanced techs like HJT.
Bifacial TOPCon panels often incorporate a transparent backsheet or are made with dual tempered glass. The advanced passivation structure of TOPCon technology is conducive to bifacial designs because it allows the panel to more efficiently capture and convert light that hits both the front and back surfaces.
Industry professionals said that TOPCon panels have a high bifacial factor, typically around 80-85%, which means they are highly effective at utilizing reflected light from the rear side. This is higher than TOPCon’s ancestor PERC, which generally has a bifacial factor of around 70%.
Latest Advances in TOPCon Solar Panel Manufacturing & Research
TOPCon solar panel technology has been a subject of significant research and development in recent years.
Lohmüller et al. demonstrated the application of thermal laser separation (TLS) and passivated edge technology (PET) to TOPCon shingle solar cells, showcasing innovative manufacturing techniques. Nijen et al. highlighted the success of TOPCon technology in front/back-contacted architectures, achieving high cell efficiencies on both n-type and p-type wafers. Furthermore, Ma et al. presented a novel tandem passivated contact approach for industrial TOPCon solar cells, indicating a promising strategy for enhancing TOPCon cell performance in large-scale production.
These achievements collectively suggest that TOPCon solar panel technology is rapidly evolving. The research community is actively exploring various innovative approaches to refine TOPCon, aiming to establish them as a leading technology in the solar sector.
Conclusion
The performance of TOPCon solar panels in real-world applications has proven the effectiveness of the advanced passivation design that underlies TOPCon technology, including the use of tunnel oxide and doped polycrystalline silicon layers.
As explained earlier, it is a friendly, high-efficiency panel technology for the industry. The 15th edition of the ITRPV forecasts that n-type TOPCon is set to overtake p-type PERC as a market leader by the end of 2024.
