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PN Junction Formation

Author: Source: Datetime: 2016-10-04 11:22:41
The band gap of the material to a large extent on the broad-spectrum characteristics of the conversion efficiency of solar energy, often the PV cell material once selected, the maximum possible conversion efficiency will be basically determined, such as monocrystalline silicon cell theoretical maximum conversion efficiency Was 24%. Various improvements in the development and design of the solar power batteries are intended to approximate the maximum conversion efficiency. According to the relevant theoretical research, the optimal band gap for solar spectrum. GaAs crystal bandgap close to the data of 1.43, use it to produce photovoltaic cells is expected to achieve high conversion efficiency.

In addition to the need to follow the law of conservation of energy, electrons must also follow the law of conservation of momentum in the transfer of electrons between the valence band and the conduction band, while the particles are running in different energy bands with different energy domains and momentums. Therefore, a complete description of the bandgap characteristics should include momentum in addition to energy. Semiconductor materials can be divided into two kinds of direct bandgap and indirect bandgap, namely the energy and momentum of both materials taking into account the bandgap structure, in which the vertical axis represents energy, horizontal axis represents momentum. solar powered portable generator can be seen that there is a certain deviation between the bottom of the conduction band of the silicon material and the top of the valence band, and the conduction band of gallium arsenide is aligned with the valence band top. The former is an indirect band gap material, while the latter is a direct band gap material.
The absorption of light by the material is similar to that of other physical processes. The variation of the irradiance with the depth of the material can be described by the following formula: The energy of the child is obtained while the momentum is obtained from other sources, but the chances of such a concurrence are minimal. Therefore, it can be seen from the bandgap structure of silicon in Figure 2-2 that the valence band position at the bottom of the conduction band should have higher kinetic energy than the valence band position, where photon excitation above the band gap is required. In the relatively concentrated range of solar power, the direct band gap material gallium arsenide absorption coefficient solar powered portable generator is greater than indirect bandgap silicon about 10 times, which means that compared to the same level of light energy absorption, direct band gap materials, the battery can do Very thin.

In pure materials, such as intrinsic semiconductors, the thermal motion of a substance generates new electron-hole pairs at all times, as well as recombination of electrons and holes. The number of electron-hole pairs in the material remains constant under thermal equilibrium conditions. When the material absorbs light to produce a new pair of electron-hole pairs, thus breaking the thermal equilibrium. These new pairs of electron-hole pairs will remain for a period of time known as the surplus carrier lifetime. The presence of surplus carriers is reflected by the photoconductivity of the material, which is exploited by photoresistors. However, it should be noted that the main mode of motion of these carriers,solar powered portable generator  regardless of how much electrons and holes are generated, is still random thermal motion and can not produce directional movement to produce current and voltage. In order to achieve the conversion of light energy into electrical energy, it is necessary to find a mechanism to orient electrons and holes, and this mechanism is the PN junction of semiconductors.

In the pure intrinsic silicon crystal, the tetravalent silicon atoms are connected to each other through four covalent bonds to form a crystal structure. The number of free electrons and holes generated by excitation is equal. If impurity elements are contaminated in the silicon crystal, they become impurity semiconductors and thus have novel properties. If doped with phosphorus, arsenic or antimony and other pentavalent elements, these elements of the five atomic valence electrons with four surrounding silicon atoms to form a covalent bond, solar powered portable generator the fifth electron easily from the nucleus and the formation of free electrons, while making The atoms themselves become non-moving positive ions. This produces a large number of impurities in the semiconductor and the proportion of impurities in the free electrons, resulting in the material the number of free electrons much more than the hole and become the main carrier (also known as the multi-carrier, the formation of II rejection semiconductors. TAG: Deployment Fixed SMA Tesvolt Unlimited Volt Army Sonnen Multi-Storage Reliability Shell Manganese 200MW Ørsted Micro