What is the structure of inorganic solar cell? Next, the structure of inorganic solar cell is introduced.
Solar cell are usually made of thin films or semiconductor wafers. Thin-film solar cell can be made of organic or inorganic materials. Inorganic solar cell are made of pn structure, and the most widely used inorganic solar cell are made of silicon. The silicon wafer is doped with a p-layer at the bottom and an n-layer at the top, and a pn junction is formed at the interface of the two regions. The electron concentration of the n-layer is greater than that of the p-layer. The electrons at the interface will move from the n-layer to the p-layer, and the holes will move in the opposite direction until the interface balance (diffusion current) is reached. The resulting space charge region is called depletion Floor. In this way, a built-in electric field directed from the n-layer to the p-layer is formed at the interface. The built-in electric field is formed by the accumulation of electrons and holes on both sides of the junction (see Figure 1). When the solar cell is exposed to light, the upper n-layer has a low electric potential, and the lower p-layer has a high electric potential. The n-layer is made thin enough to transmit as much light as possible to the junction surface. After the photon is absorbed, an electron and a hole (electron-hole pair) are excited. In other words, after a photon is absorbed, it will excite an electron to transition from the valence band to the conduction band. Only when the photon energy is greater than the battery semiconductor forbidden width, the photon will be absorbed. The built-in electric field will accelerate the movement of electrons and holes in different directions, electrons are negatively charged, and holes are positively charged. This is the process of current generation under light. The more photons that reach the pn junction, the more electron-hole pairs will be excited, and the greater the photocurrent. Moreover, the larger the surface area, the more electron-hole pairs generated, and the greater the photocurrent.
The size of the photocurrent generated by the solar cell of a certain area and temperature absorbing photons is controlled by the incident light, which is manifested in the following two aspects:
1) The intensity of incident light (number of photons).
2) The wavelength of human light (the energy of a single photon or the color of light) and the corresponding semiconductor band gap width.
In practical applications, the upper and lower electrodes of the solar cell pn junction will have ohmic contact when collecting current, and the surface is coated with an anti-reflection layer to prevent light loss caused by surface light reflection. The upper electrode is made of metal and reflects light. Therefore, the surface electrode distribution should be better designed to reduce the surface reflection as much as possible. Therefore, the electrode is designed as a stripe or interdigital shape.
Figure 2 is the structure of the wafer solar cell;
Figure 3 shows the Monocrystalline and polycrystalline silicon solar cell
The current when there is no load on both ends of the battery is the short-circuit current. The test standard is that the temperature is 25℃ and the irradiance of normal incidence is 1000W/m2. The voltage when there is no load on both ends of the battery is the open circuit voltage. The open circuit voltage does not change much with solar irradiance, and may reach its maximum value even in low light conditions. The open circuit voltage is determined by the material used to make the solar cell. The open circuit voltage of a silicon battery is approximately 0.55V.
Composition of solar photovoltaic system,You can also learn more.