 |
It is well known that amorphous silicon and microcrystalline silicon materials grown by plasma-enhanced chemical vapor deposition (PECVD) have been promising materials for thin-film solar cell fabrication.
Among them, amorphous silicon cells have a very high light absorption coefficient, and are easy to be produced on a large scale, and are currently relatively common silicon-based thin film batteries. However, the two major defects of amorphous silicon: photo-induced attenuation effect (SW effect: amorphous silicon thin film irradiated by a long time or current through the current, will produce defects in its internal and the use of film performance decline, known as SW Effects, but after summer high-temperature annealing can be partially restored photo-induced attenuation) and the absorption of long-wavelength light is not enough, to a certain extent, also affect the conversion efficiency. In order to reduce the effect of photo-induced attenuation, the amorphous silicon material is usually made into an amorphous silicon/amorphous silicon double junction structure. The first junction of amorphous silicon is used to absorb short-wavelength light waves, and the second junction is used to absorb long-wavelength waves.
The use of microcrystalline silicon material instead of amorphous silicon of the second junction will better solve the photo-induced attenuation effect, and at the same time increase the absorption of long-wavelength light to improve the conversion efficiency of the device, but the expensive equipment price makes microcrystalline silicon The mass production is limited.
Another method to increase the efficiency of a silicon thin film battery is to incorporate an appropriate amount of germanium during the deposition of an intrinsic layer of amorphous silicon (ie, an undoped region) to fabricate an amorphous silicon/amorphous silicon germanium/amorphous silicon germanium. Three-junction device. Amorphous silicon germanium not only has a high absorption coefficient of amorphous silicon, but also has the effect of microcrystalline silicon on long wavelength absorption. Therefore, amorphous silicon germanium is an ideal material for thin film solar cells.
The incorporation of an appropriate germanium element in amorphous silicon can improve the absorption of long-wavelength light. By changing the germanium content, the light absorption efficiency of the three sub-cells of the amorphous silicon germanium can be optimized, because each sub-cell of this three-junction structure absorbs the light wave of the corresponding wavelength band and can be used for each wavelength band. The light absorbs more fully. Because of its good absorption coefficient, each absorption layer can be made thin, so that the carrier (current carrier) has a shorter transmission distance and is more conducive to collection, so that a higher filling factor can be obtained and at the same time the lightening factor can be reduced. Photo-attenuation effect.
Of course, any material that has not yet been commonly used in industrialization has challenges that need to be challenged and overcome. For amorphous silicon germanium, the challenge is how to make a large area uniform amorphous silicon germanium film. As a germanium raw material gas decane is more easily decomposed than silane in the plasma field, so that the uneven distribution of germanium content in a large area of ​​the film seriously affects the conversion efficiency of the device, especially for the third subcell. A good absorption of infrared light must increase the content of cerium, which tends to increase the uneven distribution of cerium. This spatial non-uniformity is particularly pronounced in a single-chamber multi-sheet parallel mode PECVD system. Since germane is more easily decomposed, the difference in germanium content between the upper and lower parts of the device in this parallel mode is very large, resulting in a drop in the conversion efficiency of the device to unacceptable levels. For the high price of decane, single-chamber multi-chip parallel mode PECVD equipment is an ideal and economical industrialization equipment. Depositing high-quality amorphous silicon germanium thin films on this kind of equipment is very promising. In recent years, Pollock has been doing R&D and production in this area. Currently, it has been able to deposit amorphous silicon germanium thin films with good uniformity in a single-chamber, multi-chip parallel mode PECVD system.
Steel Door,Steel Security Door,Metal Door
Steel Door,Toilet doors,Wood Door Co., Ltd. , http://www.steeldoors-manufacuturer.com