Measures to improve the open circuit voltage of amorphous silicon battery
Amorphous silicon containing hydrogen: Hydrogen alloy thin films were once regarded as the most promising thin film materials for solar cells. The energy gap of the amorphous silicon film is close to the optimal forbidden band width, and because the density of defect states is low, it is easy to form effective p or n-type doping, and the barrier layer of the prepared pn junction is wider; the photo-generated carrier The life is relatively long, which is conducive to the preparation of high-performance solar cells. At the same time, the process of depositing the amorphous silicon film is not complicated, the power consumption and cost of the preparation process are low, and it is easy to realize large-scale and large-scale production. Therefore, the amorphous silicon thin film and its solar cell have received great attention. However, future research has found that solar cells made of amorphous silicon thin films will deteriorate the performance of the material after being exposed to light, and the performance of the battery will also deteriorate, especially the conversion efficiency will be reduced. Therefore, the conversion efficiency of amorphous silicon solar cells is generally less than 10%.
In order to improve the energy conversion efficiency of amorphous silicon solar cells, a variety of multi-element alloy materials have been developed on the basis of amorphous silicon-hydrogen alloys. For example, amorphous silicon-carbon-hydrogen has a large energy gap. By adjusting the carbon content, the value of the energy gap can also be changed within the range of 116-218 electron volts. For the fabricated battery, open circuit voltage and short circuit current They are larger than the corresponding parameter values ​​of amorphous silicon-hydrogen alloy batteries.
Another way to improve the conversion efficiency of amorphous silicon solar cells is to prepare multi-layer cells with variable band gaps. This type of battery is composed of multiple different pn junctions stacked into multiple layers. For solar cells, obtaining a high open-circuit voltage is exactly the opposite of the short-circuit current requirement for the band gap width of the material. When the energy gap is narrow, photons easily excite electron-hole pairs and form a large short-circuit current; but at the same time, because the potential barrier of the pn junction is small, the open circuit voltage is relatively low.
One solution to this contradiction is to design a multi-layer battery made up of different pn structures composed of different band gap materials. Because when the photon energy and the band gap energy are equal, the probability of photon absorption is the largest, materials with different band gaps can absorb light with different wavelengths in the solar spectrum, and the rubber injection machine makes the incident sunlight fully utilized. The total voltage of multiple pn junctions in series increases the open circuit voltage of the battery. However, the batteries of each layer are connected in series, and their short-circuit currents are required to be equal, which becomes the main difficulty in preparing multilayer batteries. In this way, although amorphous silicon is simpler and easier to prepare a multilayer pn junction process than single crystal silicon, there are still many unresolved designs and processes to meet the two conditions of absorbing different wavelengths of sunlight and equal short-circuit current. The problem.
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