The technical principle of thin-film solar panels is based on the photoelectric effect and the unique properties of semiconductor materials. Its core is to achieve the conversion of light energy to electrical energy through thin-film structures. The following is an analysis from three aspects: battery structure, photoelectric conversion process, and materials and processes:
Battery structure and material composition
Thin-film solar panels are composed of multiple layers of thin films stacked together, with each layer having clear functions and working in coordination.
Transparent conductive layer (TCO) : Located on the top layer of the battery, it usually adopts materials such as tin oxide (SnO₂) or zinc oxide (ZnO), which not only ensures high transmittance to visible light (>80%), but also provides good electrical conductivity, enabling the photogenerated current to be efficiently discharged.
The light-absorbing layer: It is the core part of photoelectric conversion and can be classified into cadmium telluride (CdTe), copper indium gallium selenide (CIGS), amorphous silicon (a-Si), etc. according to different materials. Take CdTe as an example. Its thickness is only 2-3 microns, but it can absorb more than 90% of the sunlight. Moreover, the band gap width (1.45eV) is highly matched with the solar spectrum and is suitable for efficient photoelectric conversion.
The electron transport layer and the hole transport layer: They are respectively responsible for collecting and transmitting photogenerated electrons and holes, reducing recombination losses. For instance, in CIGS batteries, cadmium sulfide (CdS) is typically used as a window layer to form a heterojunction with CIGS, promoting carrier separation.
Metal electrode layer: Located at the bottom of the battery, it is commonly made of metal materials such as aluminum (Al) or silver (Ag). Its function is to collect electrons transmitted to the back to form a complete current loop.
2. Photoelectric conversion process
When sunlight shines on the surface of the battery, the energy conversion mainly undergoes the following steps:
Photon absorption and excitation: After photons enter the battery, they are absorbed by the light-absorbing layer material, and their energy excited the electrons in the valence band to the conduction band, forming electron-hole pairs. Take CdTe batteries as an example. The direct bandgap characteristic of CdTe makes the generation efficiency of electron-hole pairs extremely high.
Carrier separation and transport: Under the influence of the internal electric field of the battery, electrons and holes migrate to the electron transport layer and the hole transport layer respectively. For example, in amorphous silicon cells with a p-i-n structure, the built-in electric field formed by the P-type layer and the N-type layer can effectively separate carriers and reduce the recombination probability.
Current output: The separated electrons are discharged through a transparent conductive layer and metal electrodes, forming a current in the external circuit and achieving the conversion of light energy to electrical energy.
3. Material and process innovation
Thin-film batteries enhance efficiency and stability through material optimization and process improvement:
Material selection: Different materials have unique advantages. For example, CdTe materials have low cost and high absorption coefficient, and are suitable for large-scale production. CIGS materials can optimize the bandgap width and enhance the spectral response range by adjusting the proportion of copper, indium and gallium. Amorphous silicon materials have a low preparation temperature and are suitable for flexible substrates.
Process technology: There are various thin film preparation processes, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and electrodeposition, etc. Among them, the near-space sublimation method (CSS) is used for CdTe thin film deposition, featuring high deposition rate and good thin film quality. The co-evaporation process is used in the preparation of CIGS thin films, which can precisely control the proportion of each element and improve the efficiency of the battery.
Stacked structure design: By superimposed thin film materials with different band gaps, a multi-junction battery is formed, which can broaden the spectral response range and enhance theoretical efficiency. For instance, perovskite/silicon tandem cells combine the highly efficient absorption of perovskite materials in the visible light region with the advantages of silicon materials in the near-infrared region, and the laboratory efficiency has exceeded 30%.
