Heterojunction Technology: The Future of Solar?

What is heterojunction technology?

It might sound like brand-new technology, but HJT has existed for over three decades. Japan’s Sanyo Electric (now a Panasonic company) first developed these modules in 1992. When its patent expired in 2010, HJT entered the public domain, making it possible for other companies to refine its efficiency.

Anatomy of an HJT solar cell

Heterojunction technology layers different types of silicon to capture more sunlight and generate more electricity.

HJT solar cells start with a base layer of monocrystalline silicon wafers, which are light-converting materials known for their high efficiency and long-term performance. Compared to the polycrystalline silicon used in traditional panels, monocrystalline allows for better movement of electrical charges (carriers) and is less prone to light-induced degradation.

This monocrystalline silicon wafer is then sandwiched by ultra-thin layers of amorphous silicon (a-Si), a component widely used in thin-film solar technologies. These layers act like shields. They minimize imperfections on the surface and prevent electrical charges from losing energy within the cell, keeping it working efficiently.

To be suitable for use in HJT cells, a-Si undergoes a special treatment that corrects internal flaws and allows for precise doping with specific elements. Doping fine-tunes its electrical properties and makes integrating within the HJT structure easier. More specifically, doping creates P-type and N-type regions, forming a P-N junction that converts sunlight into electricity.

Finally, a layer of Indium Tin Oxide (ITO) is applied to the cell’s surface. ITO allows most of the sunlight to pass through while efficiently collecting the electricity generated.

To complete the design, ultra-thin metal electrodes are strategically placed on the top and bottom of the cell to collect current without significantly shading the underlying silicon.

What are the benefits of heterojunction technology?

Because of its characteristics, HJT may be a stronger and more sustainable option for specific utility-scale solar projects:

Superior efficiency

HJT cells outperform current industry standards with efficiencies exceeding 22% — notably higher than the typical 20% seen with PERC modules. They can generate more electricity per square meter of solar panel, allowing you to optimize land usage or potentially reduce your solar farm’s overall footprint.

Better temperature behavior

Unlike traditional solar panels that experience performance drops under high heat, HJT has lower temperature coefficients, making it suitable for solar farms in warmer climates. Even in hot weather, there’s minimal efficiency loss, so you can rely on consistent and predictable electricity production.

Increased bifaciality

HJT modules can capture power from both sides of the panel. With bifaciality factors up to 90%, they may perform better than TOPCon and PERC systems in high albedo environments — such as in solar farms with gravel ground cover where they can harness additional reflected sunlight.

Improved longevity

HJT technology maintains over 90% power output even after 30 years. This durability also minimizes maintenance and replacement costs.

Less susceptible to Light Induced Degradation (LID)

Traditional solar panels experience a slight drop in efficiency during the initial stages of exposure to sunlight. HJT cells are less susceptible to LID because of their N-type silicon construction.

Cost-effective manufacturing

HJT cells also require fewer manufacturing steps and employ lower-temperature processes. This may reduce your project’s overall energy consumption and carbon emissions.

Single junction vs. heterojunction technology: What's the difference?

Single junction technology is the most prevalent type of solar cell. As its name suggests, it uses a single layer of semiconductor material (typically silicon) to convert sunlight into electricity. This material’s band gap limits the range of sunlight wavelengths it can absorb.

In contrast, heterojunction technology uses two different semiconductor materials with different band gaps. This design does two things: it broadens the spectrum of sunlight colors the cells can capture and amplifies the cell’s ability to convert sunlight into electricity.

In terms of theoretical efficiency, these two technologies are almost equal: Single junction cells reach 29.2% and heterojunction cells reach 29.4%. However, heterojunction cells win when it comes to practical efficiency because they last longer and handle heat better. And, as production costs continue to decline, HJT may be on its way to becoming the leading choice for high-performance silicon solar cells.

What does heterojunction technology's future hold? 

Many PV experts predict that it will soon dethrone single-junction PERC, the current king of solar panels.

The numbers seem to point that way. HJT’s production cost should drop to $0.20 per watt in five to six years — that’s less than half the $0.46 per watt it costs to produce complex PERC systems.

Given these market trends, it’s safe to say that HJT’s future is optimistic. If successful, HJT could lead the charge in the next era of solar power. Even if adoption takes longer than expected, the fierce competition will fuel continuous breakthroughs across the solar industry.

Optimize your solar project’s potential with RatedPower

Are you wondering if HJT is right for your project? RatedPower is the most efficient way to compare and analyze different PV module technologies for your utility-scale solar power plant. Our platform’s precise simulation capabilities allow you to assess performance, power voltage, and current coefficients in one place.

RatedPower’s high-performance features simplify solar panel selection. Set different technologies side-by-side — considering factors like efficiency, cost, and land use — to find the best balance between performance and affordability.

With our intuitive tools, you can define specific capacities, compare installed areas, calculate light-induced degradation, and much more in a few clicks. RatedPower can even automatically generate energy yield reports and detailed bills of quantities to help you communicate your project’s technical merits and value proposition to investors.

See RatedPower in action as our product manager, Jorge Masa, demonstrates how to compare different modules using our platform.