Buying Guide Of HJT Solar Cell

What is a Heterojunction Solar Panel?

Heterojunction (HJT) solar panels are similar to standard homojunction panels in their assembly, but the key difference lies in the structure of the solar cell itself. HJT technology integrates multiple materials and advanced cell designs to enhance efficiency and performance. Here's a breakdown of the materials, structure, and manufacturing process used in HJT panels:

 

Key Materials Used in HJT Cells:

 

Crystalline Silicon (c-Si):

Crystalline silicon is a widely used material for standard homojunction solar cells. In HJT cells, only monocrystalline silicon (which has higher purity and efficiency) is used, unlike conventional panels that may also utilize polycrystalline silicon.

 

Amorphous Silicon (a-Si):

Amorphous silicon, commonly used in thin-film PV technology, plays a crucial role in HJT cells. Despite its natural density defects, the hydrogenation process improves its properties, transforming it into hydrogenated amorphous silicon (a-Si

). This version is easier to dope and has a wider bandgap, making it ideal for HJT cells.

 

Indium Tin Oxide (ITO):

ITO is the material of choice for the transparent conductive oxide (TCO) layer in HJT cells. It provides excellent reflectivity and conductivity, making it an efficient external layer for energy capture. However, research is underway to find indium-free alternatives to reduce costs without compromising performance.

 

Structure of HJT Solar Cells

HJT cells combine layers of monocrystalline silicon and thin-film amorphous silicon, creating a hybrid design that enhances both light absorption and energy conversion. The monocrystalline silicon serves as the main substrate, while the amorphous silicon layers act as passivation layers, reducing defects and improving efficiency. Additionally, the TCO layer (often made of ITO) ensures good conductivity and allows sunlight to pass through.

Advantages of HJT Technology

The combination of these materials allows HJT solar panels to achieve higher efficiency and better performance compared to traditional solar technologies, particularly in terms of bifaciality, low-light performance, and long-term stability.

 

The absorber layer of a heterojunction solar cell consists of a crystalline silicon (c-Si) wafer (blue layer) sandwiched between two thin intrinsic hydrogenated amorphous silicon (i-a-Si:H) layers (yellow layers). On top of each intrinsic layer, doped hydrogenated amorphous silicon (a-Si:H) layers (red and green layers) are added. The number of Transparent Conductive Oxide (TCO) layers depends on whether the HJT cell is monofacial or bifacial. In monofacial cells, the rear side is covered by a metal layer, which acts as the conductor.

 

How Do Heterojunction Solar Panels Work?

 

Heterojunction (HJT) solar panels operate on the same basic principle as other photovoltaic (PV) modules, utilizing the photovoltaic effect to convert sunlight into electricity. However, they incorporate a unique structure with three layers of absorbing materials, combining thin-film and traditional PV technologies for improved efficiency.

 

How the Process Works:

 

When sunlight strikes the panel, photons are absorbed by the cell's P-N junction, exciting electrons and creating electron-hole (e-h) pairs. The excited electrons move to the conduction band, where:

 

1. Electron Excitation: A photon impacts the absorber layer at the P-N junction, exciting an electron and causing it to move to the conduction band, forming an electron-hole pair.

 

2. Current Flow: The excited electron is collected by the terminal connected to the P-doped layer, generating electric current that flows through the load.

 

3. Electron Recombination: After passing through the load, the electron returns to the rear contact of the cell and recombines with a hole, completing the electron-hole cycle. This process repeats continuously as electricity is produced.

 

Reducing Surface Recombination for Higher Efficiency:

 

In conventional crystalline silicon (c-Si) PV modules, a phenomenon known as surface recombination can reduce efficiency. This happens when excited electrons recombine with holes at the material's surface before being collected, preventing the generation of electricity. HJT cells minimize surface recombination by adding a passivating semiconductor film with a wider bandgap, made from hydrogenated amorphous silicon (a-Si:H), between the highly recombinative contacts and the silicon wafer. This buffer layer slows the flow of charges enough to create high voltage while preventing recombination, thereby increasing the overall efficiency.

 

Three-Layer Photon Absorption:

 

HJT solar cells absorb photons and convert them into electricity through a multi-step process involving three semiconductor layers:

 

1. The outer a-Si:H layer first absorbs incoming photons and converts them into electricity.

2. Most of the sunlight is absorbed by the c-Si layer, which has the highest conversion efficiency of the materials in the cell.

3. Any remaining photons are absorbed by the rear a-Si:H layer, completing the process.

 

This three-step absorption mechanism allows HJT cells to achieve solar efficiencies as high as 26.7%, outperforming traditional monofacial cells.

 

Benefits of Heterojunction Solar Panels

Heterojunction (HJT) solar panels offer several key advantages due to their advanced technology, making them highly promising in the solar industry. Here are the major benefits:

 

High Efficiency

HJT panels achieve a conversion efficiency of 26.07% for monofacial modules and over 30% for bifacial designs. This makes them one of the most efficient solar technologies available, ideal for applications with limited space or high energy demands.

 

Excellent Temperature Coefficient

HJT technology is less sensitive to temperature changes, maintaining high performance even in hot environments where standard crystalline silicon (c-Si) modules typically suffer reduced efficiency. This makes HJT panels especially suitable for regions with high temperatures.

 

High Bifaciality

HJT cells boast a bifaciality factor of 92%, making them highly effective in bifacial panel designs. This feature is increasingly popular for utility-scale installations that benefit from reflected light (albedo), maximizing energy output from both sides of the panel.

 

Streamlined Manufacturing Process

Although HJT cells require a few additional steps in the manufacturing process, this doesn’t significantly increase costs. The process involves only 5-7 steps, and as equipment costs continue to decrease, HJT technology shows strong potential for widespread adoption in the future.

Why choose us

Beijing Shan Hu International Technology Co.,Ltd. is a professional enterprise involved in manufacturing and marketing the best quality solar panels and provide solutions for a wide range and variety of customers home and abroad. It is located in Beijing Economic-Technological Development Area, China.

The company was established in 2020, now over 80% of our commercial managers and engineers have many years of solution experiences. At present, the company's business scope covers multiple countries and regions including China, Europe, America, Southeast Asia, and Africa. Beijing Shanhu International has always adhered to the mission of promoting the energy revolution process with photovoltaic technology and benefiting all mankind with solar energy. Aiming to create a series of digital comprehensive solutions for green energy, including green buildings, green travel, green industrialization, and smart home energy. We hope that through our exploration and efforts, more people can enjoy the value of sunshine and create a green energy world with the radiance of the sun.