Solar power generation, as a leading clean energy solution, has garnered significant attention from the industry. If you're interested, let’s dive into the structure of solar cells and the related photovoltaic materials.
Solar power generation, often referred to as solar cells, directly converts sunlight into electricity. In solar panels, photons from the sun dislodge electrons from the atomic bonds of semiconductor materials. When these electrons are forced to move in the same direction, they generate an electric current that can either power electronic devices or be fed into the electrical grid.
Since French physicist Alexandre-Edmond Becquerel first theorized photovoltaic technology in 1839, solar power generation has been a key topic of research. Today, with major research teams from the U.S., Japan, and Europe accelerating the commercialization of their solar systems, the international market for the photovoltaic industry continues to expand.
Photovoltaic Modules
Though the materials in photovoltaic systems vary, all modules consist of several layers from the front-facing side to the back. Sunlight first passes through a protective layer (usually glass), then through a transparent contact layer into the cell itself. At the center of the module is the absorber material, which captures photons to generate electrical current. The type of semiconductor material used depends on the specific needs of the photovoltaic system.
Beneath the absorber material is the back metal layer, which completes the electrical circuit. Below the metal layer is a composite film layer, which waterproofs and insulates the module. Photovoltaic modules are often equipped with an additional protective backing layer made from glass, aluminum alloy, or plastic.
Semiconductor Materials
Semiconductor materials in photovoltaic systems can be silicon, polycrystalline thin films, or monocrystalline thin films. Silicon materials include monocrystalline silicon, polycrystalline silicon, and amorphous silicon. Monocrystalline silicon, with its regular structure, has a higher photovoltaic conversion efficiency than polycrystalline silicon.
In amorphous silicon, silicon atoms are randomly distributed, resulting in lower conversion efficiency compared to monocrystalline silicon. However, amorphous silicon can capture more photons, and alloying it with elements such as germanium or carbon can enhance this property.
Copper indium diselenide (CIS), cadmium telluride (CdTe), and thin-film silicon are commonly used polycrystalline thin-film materials. High-efficiency materials such as gallium arsenide (GaAs) often incorporate monocrystalline silicon thin films. These materials are selected for specific photovoltaic applications based on unique properties such as crystallinity, band gap size, absorption capabilities, and ease of processing.
External Factors Affecting Semiconductors
The atomic arrangement in a crystal structure determines the crystallinity of semiconductor materials, which directly impacts the charge transport, current density, and energy conversion efficiency of solar cells. The band gap of semiconductor materials refers to the minimum energy required to move electrons from a bound state to a free state (allowing for conduction). The band gap, typically denoted as Eg, describes the energy difference between the valence band (low energy) and the conduction band (high energy).
The absorption coefficient quantifies the distance a photon of a particular wavelength can penetrate a medium before being absorbed. It is determined by the material of the cell and the wavelength of the absorbed photon.
The cost and ease of processing various semiconductor materials and devices depend on numerous factors, including the type and scale of materials used, production cycles, and the migration characteristics of the cell in the deposition chamber. Each factor plays a crucial role in meeting specific photovoltaic generation needs.
