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Quantum Physics Foundation Of Photovoltaic Effect

Author: Source: Datetime: 2016-10-04 11:22:17
When the light is irradiated onto a substance may be reflected, transmitted or absorbed, which absorbs the meaning of the incident light in the photon energy conversion to another form of energy, such as heat. However, solar power batteries certain substances have properties that make it possible to convert the energy carried by photons into electrical energy. One result of the absorption of photons is the transfer of energy carried by the atoms in the absorption of electrons, this conversion follows the law of conservation of momentum and energy conservation law. Depending on the energy carried by the photon, the electrons in the atom can be elevated from a low energy state to a high energy state, or even become free electrons out of the atom, possibly forming electrons under the action of an external condition such as temperature, diffusion and electric field mobile.

According to quantum theory, an isolated atom of electrons run on a number of different levels of orbit (or shell), in different orbits of electrons with different energy. The electrons in the low-level orbit can be transited to the high-energy level orbit by some mechanism, such as light, and the electrons in the high-energy orbit will release energy at the same time. In the crystal composed of many atoms, electrons can be shared by many atoms and migrated in the atoms due to the intersection of high-level electron orbitals of many atoms, so that the electrons in the same energy state produce tiny energy differences solar powered portable generator, and This corresponds to the energy level extended to band. The range between energy bands that can be occupied by electrons is not allowed to be occupied by electrons, and this range is called forbidden band. The electrons usually fill the lower band with the band to make it full, and then occupy the higher energy band outside the layer. In particular, any band occupied by electrons is called an empty band.
The electrons in the full band can not participate in the macroscopic conductive process, and the electron in the valence band can pass through the forbidden band to jump to the conduction band to participate in the conductive process. Conducting conductor or semiconductor conduction is through the movement of charged particles to form the current, the carrier of this current is called carrier. The carriers in the conductor are free electrons, and the carriers in the semiconductors are negatively charged electrons and positively charged holes. Semiconductor material is characterized by its absolute zero when it is the perfect insulator, but when the temperature rise will produce carriers. As shown in Figure 2-1, all valence electrons are located in the valence band at absolute zero and there is no electrons in the conduction band, and in this state no conduction process is possible. When the temperature rises, some of the valence band electrons get enough energy to move to the conduction band, in the semiconductor these electrons are actually leaving the covalent bond of the semiconductor material, so that the price of the band to produce the so-called "empty hole". Note that the electrons of the conduction band and the holes of the valence band are generated in pairs, so the electrons and holes are called electron holes. The directional flow generated by the two kinds of carriers under certain action will constitute the semiconductor material in the Conductive process.

The electrons in the valence band of the material are excited by the photon to transition to the conduction band, creating a hole in the valence band, and the process of annihilation of the photon body is called light absorption. The process of absorbing photons in materials has the following characteristics: Photon absorption is the premise that its energy must exceed the material bandgap energy. The photons with energy reaching and exceeding the bandgap are likely to be absorbed and produce electron-hole pairs. The photons with energy exceeding the bandgap can only produce an electron-hole pair, and the excess energy will be lost in the material and converted into heat solar powered portable generator. In other words, no matter how much energy the photon carries, the generation of the electron-hole pairs takes only a part of the bandgap equal to the bandgap, and the rest can only be converted to heat; depending on the characteristics of the material such as thickness, the energy is low The light in the band gap is converted into heat in the material and the other part is passed through the material, i.e., the material is "transparent" to this portion of the light.

Sunlight has a continuous spectrum of ultraviolet to visible light from the infrared spectrum, the power spectrum describes the sun at all different wavelengths of photon energy and the number of photons multiplied. The high-power part of the solar spectrum is mainly distributed in the visible and near-infrared parts, the peak at 0.5! The solar powered portable generator of the left and right green-light regions is 2 ~ 6 Å. In the solar power generation system, it is desirable for the photovoltaic cells to obtain the maximum absorption from the solar spectrum to obtain the best conversion efficiency, in which the band gap of the semiconductor material is one of the key factors affecting the conversion efficiency. TAG: Multi-Storage Reliability Shell Manganese 200MW Ørsted Micro ABB Programs Volvo 65MW Porsche Largest Volkswagen Lease