![]() The most popular doping uses n-type c-Si wafers. Heterojunction solar cells can be classified into two categories depending on the doping: n-type or p-type. Classification of heterojunction solar cells A specially curated silver paste at low temperatures is used, through a copper electroplating or screen printing process, to place the electrodes on the cell. The metallization process diverges from regular manufacturing processes because the hydrogen in a-Si:H limits the temperatures to a maximum of 200-220✬. An alternative process uses Reactive Plasma Deposition (RPD) to apply the TCO layer, but this is a less popular option. The second part of the deposition process uses Physical-Vapor Deposition (PVD) through sputtering to apply ITO, forming the TCO layer of the heterojunction solar cell. There are two methods often used for wet-chemical processing, the RCA method involving the use of concentrated sulfuric acid and hydrogen peroxide, and a cost-effective alternative applying an ozone-based process, obtaining similar results.Īfter the wet-chemical processing, the deposition process using Plasma-Enhanced Chemical Vaporization Deposition (PECVD) is applied, depositing a-Si layers on both sides of the wafer-based layer. Performing this process with extreme delicacy will result in high-quality c-Si layers, which translates to higher efficiency.ĭuring the wet-chemical processing, organic and metal impurities are removed from the c-Si wafer. The wafer processing involves cutting the c-Si cells with a diamond-based saw. There are several steps involved in the manufacturing process of the heterojunction solar cell. Manufacturing of a heterojunction solar cell The number of TCO layers varies depending on the HJT cell being monofacial or bifacial, with the rear layer being a metal layer acting as the conductor for monofacial heterojunction cells. The absorber layer of the heterojunction solar cell encloses a c-Si wafer-based layer (blue layer) placed between two thin intrinsic (i) a-Si:H layers (yellow layer), with doped a-Si:H layers (red & green layers) placed on top of each a-Si:H (i) layer. Structure of HJT solar cell - Source: De Wolf, S. HJT technology, instead, combines wafer-based PV technology (standard) with thin-film technology, providing heterojunction solar cells with their best features. Standard (homojunction) solar cells are manufactured with c-Si for the n-type and p-type layers of the absorbing layer. Structure of the heterojunction solar cell The reflectivity and conductivity properties of ITO make it a better contact and external layer for the HJT solar cell. Indium Tin Oxide is the preferred material for the transparent conductive oxide (TCO) layer of the heterojunction solar cell, but researchers are investigating using indium-free materials that will reduce costs for this layer. While a-Si on itself has density defects, applying a hydrogenating process solves them, creating hydrogenated amorphous silicon (a-Si:H), which is easier to dope and has a wider bandgap, making it better for creating HJT cells. ![]() There are two varieties of c-Si, polycrystalline and monocrystalline silicon, but monocrystalline is the only one considered for HJT solar cells since it has a higher purity and therefore more efficient.Īmorphous silicon is used in thin-film PV technology and is the second most important material for manufacturing heterojunction solar cells. ![]() There are three important materials used for HJT cells:Ĭrystalline silicon is regularly used to create standard homojunction solar cells, seen in conventional panels. Materials required to manufacture a heterojunction solar cell To understand the technology, we provide you with a deep analysis of the materials, structure, manufacturing, and classification of the HJT panels. Heterojunction solar panels are assembled similarly to standard homojunction modules, but the singularity of this technology lies in the solar cell itself.
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