What Are HJT Solar Cells?

Heterojunction (HJT) technology has been overlooked for many years, but over the past few years it has been evolving and showing its true potential. Heterojunction addresses some of the common limitations of standard photovoltaic (PV) modules, such as reducing the compounding process and improving performance in hot climates.

HJT solar cell is assembled similarly to standard homojunction modules, but the uniqueness of the technology lies in the solar cells themselves. To understand the technology, we provide you with an in-depth analysis of the materials, structure, fabrication and classification of heterojunction panels.

Materials needed to manufacture HJT solar cells

Heterojunction cells have three important materials.

1. Crystalline silicon (c-Si)

2. Amorphous silicon

3. Indium tin oxide (ITO)

Crystalline silicon is typically used to make standard homojunction solar cells, as seen in conventional panels. c-Si comes in two varieties, polycrystalline and monocrystalline, but monocrystalline is the only one considered for heterojunction solar cells because it has a higher purity and therefore higher efficiency.

Amorphous silicon is used in thin-film photovoltaic technology and is the second most important material for manufacturing heterojunction solar cells. Although a-Si itself has density defects, they can be resolved by applying a hydrogenation process that produces hydrogenated amorphous silicon (a-Si:H), which is easier to dope and has a wider band gap, making it more suitable for heterojunction cell fabrication.

Indium tin oxide is the material of choice for the transparent conducting oxide (TCO) layer of heterojunction solar cells, but researchers are investigating the use of indium-free materials to reduce the cost of the layer. the reflectivity and conductivity properties of ITO make it a better contact and outer layer for heterojunction solar cells.

The structure of heterojunction solar cells

The absorber layer of a heterojunction solar cell encloses a c-Si wafer-based layer placed between two thin intrinsic (i) a-Si:H layers, with a doped a-Si:H layer placed on top of each a-Si:H(i) layer. the number of TCO layers depends on whether the heterojunction cell is single-sided or double-sided, with the latter layer being a metal layer that acts as a conductor for the single-sided heterojunction cell.