Solar Power Batteries Technology
Author: Source: Datetime: 2016-10-05 00:20:31
In the discussion so far, an absorbed photon produces an electron-hole pair. If a material has an intermediate band between the conduction band and the valence band and is inserted between the two general semiconductors, it is possible for the material to absorb two less energy photons and produce a photon with the combination of the two photons Energy of an electron-hole pair. The first photon lifts an electron to the intermediate band and creates a hole in the valence band, while the second photon lifts the electron from the intermediate band to the conduction band. The key is to find such an intermediate band material that can hold the electrons on the intermediate band and wait for the photons with the appropriate energy to hit the material. To support this electron transport process, the electronic energy state of the material needs to be half empty and half electron occupied. Compounds may fulfill this technique and allow the theoretical conversion efficiency of the cell to reach 63,2%.
If the battery uses a lot of layers of laminated structure, the bandgap of the largest material on the top, and down the layers of the bandgap layer by layer, you can reach the theoretical conversion efficiency of 86.8%. A 4-layer cell with an area of 10 A has been fabricated with an efficiency of 35.4% and a theoretical maximum efficiency of 41.6%. The hot-carrier battery uses the method of avoiding the inelastic collisions of the photogenerated carriers to reduce the energy loss, and the limit efficiency is about 86.8%. The excess energy of the photon confers a high thermal energy on the carrier. These "hot carriers" first reach a certain thermal equilibrium by the collision between the carriers after about a few picoseconds after being excited. The collision of these carriers does not result in energy loss, but causes redistribution of energy between the carriers. Then, after a few nanoseconds, the carriers collide with the lattice and transfer the energy to the lattice. After a few microseconds of light, if the electrons and holes can not be effectively separated into positive and negative, they will re-composite.
Hot-carrier solar power batteries are required to collect electrons and holes before they cool down to the positive and negative sides of the cell. So the absorption layer must be very thin, about tens of nanometers. The use of superlattice structure as the absorption layer can delay the carrier cooling, increase the thickness of the absorber layer, improve the absorption of light. An alternative to changing the material bandgap is to change the energy distribution of the emission spectrum. Some materials have the ability to absorb two photons with different energies and emit their combined energy with a single photon. In addition some of the material can be absorbed by a high-energy photon energy to two low-energy photon emitted. These phenomena are similar to band up-conversion and down-conversion in a wireless communication circuit.
This method is reflected in the optical shape of the spectrum is changed, the spectrum of human light can be compressed to a relatively narrow range and increase its strength, thereby improving the conversion efficiency of the battery. One advantage of this method is that it is not necessary to place the optical up-down converter with the photovoltaic cell, simply by placing it between the source and the solar power batteries. TAG: Ireland Hawaii Duke 100Ah 48V telecom Malta Battery-Box Passenger NTPC Containerized Off-Grid Code Building California
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