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What Is Heterojunction（HJT）Solar?

HJT is the acronym for hetero-junction solar cells. Introduced by Japanese company Sanyo in the 1980s, then acquired by Panasonic in 2010s, HJT is considered as a potential successor to the popular PERC solar cell as of the time of writing, besides other technologies such as PERT and TOPCON.

Due to HJT’s fewer number of cell processing steps, and a much lower cell processing temperatures, this architecture has the potential to simplify the current solar cell manufacturing lines that are currently heavily based on PERC technology.
How does HJT work?
Heterojunction solar panels are composed of three layers of photovoltaic material. HJT cells combine two different technologies into one: crystalline silicon and amorphous “thin-film” silicon.

The top layer of amorphous silicon catches sunlight before it hits the crystalline layer, as well as light that reflects off the below layers. However, monocrystalline silicon, the middle layer, is responsible for turning most of the sunlight into electricity. Lastly, behind the crystalline silicon is another amorphous thin-film silicon layer. This final layer captures the remaining photons that surpass the first two layers.

Figure 1: p-type PERC vs n-type HJT solar cell

As shown figure 1, HJT is very different to the popular PERC structure. As a result, manufacturing processes between these two architectures are very different. Compared to n-PERT or TOPCON, which can be upgraded from the current PERC lines, HJT requires significant capital investment in new equipment to start mass productions.

HJT demonstrates high solar cell efficiency thanks to the high quality hydrogenated intrinsic amorphous Si (a-Si:H in Figure 1) that can provide impressive defect passivation to both the front and rear surface of Si wafers (both n-type and p-type polarity).
The use of ITO as transparent contacts also improves current flows, while also acting the anti-reflection layer to provide optimal light capturing. Moreover, ITO can also be deposited via sputtering at low temperature, thus avoiding the re-crystallisation of the amorphous layer that will impact the passivation quality of the materials on the bulk Si surface.

In spite of its processing challenges and high capital investments, HJT is still an attractive technology. This technology demonstrates the ability to achieve >25% solar cell efficiency, compared to ~22% shown by TOPCON, PERT and PERC technologies.
Advantages of Heterojunction Solar Cells

Here are a few key advantages of using HJT solar cells for your building:

Higher efficiency

JG Solar HJT panels that are currently on the market have efficiencies ranging from 21.0%–22.8%. This is a massive improvement compared to other conventional monocrystalline cells. It is by far the highest solar panel efficiency of HJT mass production.

Cost savings

The amorphous silicon used in HJT panels is a cost-effective photovoltaic technology. This thin-film solar requires shorter manufacturing compared to other technologies. Because of its simplified manufacturing process, HJT has the potential to be more affordable than alternative solutions.

Resilience and adaptability

This technology was developed for excellent production capabilities, even in extreme weather conditions. HJT panels have lower temperature coefficient than conventional solar panels, ensuring high performance at elevated external temperatures.

Life expectancy

On average, thin-film photovoltaic modules have a life expectancy of up to 25 years, while HJT solar cells can remain fully functioning well over 30 years.

The Future of HJT Solar

According to the ITRPV 2019 report, HJT cells are expected to gain a market share of 12% by 2026 and 15% in 2029.
Given the several advantages of HJT solutions, it is likely that more companies will continue to adopt this technology in the near future. Because the HJT manufacturing process requires four fewer steps than PERC technology, there is potential for significant cost savings. While PERC has been a popular option in the industry for many years, its complex manufacturing process cannot compete with HJT. In addition, PERC does not offer HJT’s high temperature performance benefit.

Sputtering Targets: The King Of Semiconductor Chip Materials

When we examine the long-term plan of "Made in China 2025," the path to economic transformation and upgrading becomes remarkably clear. The semiconductor industry, in particular, stands as a vanguard for improving economic quality and is expected to enter a golden development period in the next decade. Advanced semiconductor technologies play a crucial role in national security, intensifying the demand for autonomous and controllable capabilities.

The pressure on raw material prices and the escalating trade tensions between China and the United States have raised alarms for domestic manufacturers. The semiconductor industry has recognized that to achieve the goal of "autonomous control," it must gain control over upstream raw materials and equipment.

1.
In the chip industry, which aims to reach the pinnacle of high technology, sputtering targets are essential raw materials for the manufacturing of very large-scale integrated circuits (VLSI). Sputtering targets utilize ions generated by an ion source, which, under high vacuum conditions, are accelerated and formed into a high-speed ion beam. This beam bombards the surface of a solid material, resulting in an exchange of kinetic energy between ions and surface atoms, causing the atoms on the solid surface to depart and deposit onto a substrate's surface. The solid material being bombarded serves as the raw material for the sputtering process and is referred to as sputtering targets. Targets are the core materials in the sputtering process.

2.
Inside the individual components of integrated circuits, there are layers consisting of a substrate, an insulating layer, a dielectric layer, a conductor layer, and a protective layer. Among these, the dielectric layer, conductor layer, and even the protective layer require the sputtering coating process. Therefore, sputtering targets are one of the core materials for fabricating integrated circuits. In the field of integrated circuits, the sputtering targets used for coating primarily include aluminum targets, titanium targets, copper targets, tantalum targets, tungsten titanium targets, and more. These targets demand very high purity, typically at or above 5N (99.999%).

3.
Cu sputtering targets for semiconductor

4.
Al sputtering targets for semiconductor

High-purity metal sputtering targets are primarily applied in wafer manufacturing and advanced packaging processes. Taking chip manufacturing as an example, we can see that the transformation from a silicon wafer to a chip involves seven major production processes: diffusion (Thermal Process), photolithography (Photo-lithography), etching (Etch), ion implantation (Ion Implant), dielectric deposition (Dielectric Deposition), chemical mechanical polishing (CMP), and metallization (Metalization). Each of these steps corresponds to specific equipment, materials, and processes. Sputtering targets are used in the "metallization" process, where high-energy particles are used to bombard the target material in a thin film deposition device. This process forms specific functional metal layers on the silicon wafer, such as conductive layers and barrier layers.

What are sputtering targets?
Sputtering targets are the raw materials used for depositing thin films through Physical V***r Deposition (PVD) techniques. PVD processes are divided into sputtering and evaporation methods.

Sputtering is a process that utilizes ions generated by an ion source. These ions are accelerated and formed into a high-speed ion beam in a vacuum. They bombard the surface of a solid target material, resulting in kinetic energy exchange between the ions and the surface atoms of the solid. This causes atoms from the solid target to leave and deposit onto the substrate's surface, forming a nano (or micro) thin film. The solid material that is being bombarded serves as the raw material for PVD thin film deposition and is referred to as a sputtering target. The quality of the target material plays a crucial role in determining the performance of the thin film.

Classification of sputtering targets
Sputtering targets come in various types and find extensive downstream applications. They are primarily classified based on three criteria: shape, chemical composition, and application field.

Shape Classification: Sputtering targets are primarily categorized into three shapes: rectangular targets, square targets, and circular targets.

Chemical Composition Classification: Sputtering targets can be classified based on their chemical composition into the following categories: metal targets, alloy targets, and ceramic compound targets.

Application Field Classification: Targets are also classified based on their intended application fields, which include semiconductor chip targets, flat-panel display targets, solar cell targets, information storage targets, tool modification targets, and electronic device targets.

In terms of application scenarios, sputtering targets are mainly used in fields such as semiconductor chips, flat-panel displays, solar cells, information storage, tool modification, and electronic devices. Among these, semiconductor chips, flat-panel displays, and photovoltaic cells have particularly high requirements for target purity and stability and typically use high-purity targets. Semiconductor chips have the strictest requirements, often demanding target purity levels of 99.9995% (5N5) or higher, while flat-panel displays typically require target purity at the 99.999% (5N) level, and photovoltaic cells generally require target purity at 99.99% (4N) or higher.

Industry Chain Analysis

From the perspective of the target material industry chain, the production of sputtering targets can be divided into four stages: metal purification, target manufacturing, sputter coating, and terminal applications.

1. Metal purification

In the upstream materials segment, metals such as aluminum, copper, tantalum, and titanium are purified through metal purification processes to produce high-purity metals, which serve as raw materials for target manufacturing. High purity, and even ultra-high purity, metals are the foundation for producing high-purity metal targets. Elevated impurity levels in targets can directly impact the performance of deposited thin films. Therefore, the technology of purifying metals to achieve high purity is one of the core barriers in the target material industry. Simple metal purification alone cannot meet the stringent requirements of target materials.

2. Target manufacturing

The target manufacturing stage involves processing high-purity metals to create sputtering targets. Within the sputtering target production chain, the target manufacturing stage demands the highest requirements for production equipment and technological processes. The quality of sputtered thin films has a significant impact on the quality of downstream products.

During the target manufacturing stage, the first step is to design the processes based on the performance requirements of the target material for its intended downstream applications. Subsequently, various processes including repeated plastic deformation, heat treatment to control parameters like grain size and crystal orientation, water cutting, machining, metallization, quality testing, and ultrasonic cleaning are carried out.

The target manufacturing process involves intricate and numerous steps, and the management of process flow and the level of manufacturing technology directly influence the quality and yield of sputtering targets.

3. Sputter coating

During the sputter coating process, sputtering targets need to be installed in specialized sputtering equipment to carry out the sputtering reaction. Sputtering machines are highly specialized and precise. Specifically, coating equipment can generally be divided into five main components: the vacuum formation system, the ion source and deposition system, the deposition environment control system, the monitoring system, and the drive mechanism system.

Terminal applications
The sputter-coated substrates find their way into various terminal applications across industries. These applications include semiconductor manufacturing, flat-panel displays, solar cell production, information storage devices, tool modification processes, and electronic device production. The choice of sputtering target material and its quality directly impacts the properties and performance of the final products in these industries.

Each stage in the sputtering target industry chain is critical to ensuring the quality and performance of the final sputter-coated products used in diverse high-tech applications.

According to data, in the global sputtering target downstream markets in 2020, flat-panel displays held the highest share at 34%, followed by recording media and solar cells at 29% and 21%, respectively, with semiconductors accounting for 10%. In the Chinese sputtering target application market, flat-panel displays and recording media also had significant shares, reaching 49% and 28%, respectively, while semiconductors and solar cells accounted for 9% and 8%, respectively. The continuous development and expansion of downstream application markets will provide new growth opportunities for the sputtering target market and drive the development of the sputtering target industry.