This chapter introduces the structure and advantages of amorphous silicon solar cells.
In 1976, Karlsson and Luonsky reported the birth of amorphous silicon (also known as a-Si) thin-film solar cells. At that time, the photoelectric conversion efficiency of the small-area samples was only 2.4%. After more than 30 years, not only did the amorphous silicon cell be commercialized first, but also the amorphous silicon solar cell has now developed into one of the most practical and cheapest solar cell varieties. First, of course, it is also the current large-scale thin-film battery.
(1) The basic structure of amorphous silicon solar cells
Because amorphous silicon has multiple defects, doping tends to further increase the defect density. The basic structure of amorphous silicon solar cells is not a PN junction but a PIN junction doped with boron to form a P region, doped with phosphorus to form an N region, and I is an intrinsic layer that is non-impurity or lightly doped with B. The heavily doped P and N regions form an internal potential inside the battery to collect charges. At the same time, the two can form contact with the conductive electrode to provide electric power to the outside. Zone I is the photosensitive zone, and the ratio of photoconductivity/dark conductance is in the range of 105~106. The photo-generated electrons and photo-generated holes in this area are the source of photovoltaic power. The long-range disorder of the amorphous silicon structure destroys the photoelectron transition of crystalline silicon, changing it from an indirect band gap material to a direct band gap material. The photon absorption coefficient is very high, and the light absorption in the sensitive spectrum is exhausted. Therefore, the thickness of the PIN structure of the amorphous silicon cell is about 500nm and the thickness of the P and N layers as the dead light absorption zone is limited to the order of 10nm.
(2) Unique advantages of amorphous silicon solar cells
Amorphous silicon solar cells have many unique advantages, which are mainly manifested in the following aspects.
①Less raw material consumption and low manufacturing process cost
The production of amorphous silicon batteries consumes less raw materials and can use cheap substrates and flexible material substrates, because these substrate materials (such as glass, stainless steel, plastic, etc.) are cheap. The thickness of the silicon film is only a few hundred nanometers, and the amount of expensive pure silicon materials is very small. During production, the heating temperature is low, only 100~300℃. The power consumption of production is small, and it is easy to realize large-scale and automated production.
②Easy to form large-scale production capacity
This is because the core process is suitable for the production of large-area, amorphous silicon alloy films without structural defects; the PIN junction and the corresponding laminated structure can be realized only by changing the gas phase composition or the gas flow rate, and the production is easy to be automated.
③Amorphous silicon solar cells with multiple varieties and wide applications are easy to realize integration. The device power, output voltage, and output current can be freely designed and manufactured, making it easier to produce a variety of products suitable for different needs. Due to the high light absorption coefficient and low conductivity, it is suitable for making low-power power supplies for indoor use, such as watch batteries, calculator batteries, etc. Due to the good mechanical properties of amorphous silicon film, it is suitable for making light and large batteries on flexible substrates. The manufacturing method is flexible and diverse, and can be used to manufacture building-integrated batteries, which is suitable for the installation of household rooftop power stations.
④Good performance, its radiation resistance is 50-100 times higher than that of crystalline Si cells, and the efficiency of amorphous silicon cells with reduced conversion efficiency can be restored to 80%-97% of the original value after annealing at 130~175℃. Performance that other batteries do not have. Amorphous silicon battery also has the highest efficiency/mass ratio (that is, the material is light and the efficiency is relatively high), up to 2500W/kg (using polymer flexible substrate), and the conversion efficiency is 8% of the battery components, using stainless steel The large-area component of foil (length 804.5m, width 35cm, thickness 0.01250.025mm), the power/mass ratio can reach 600W/kg, while the general crystalline Si battery is 40~100W/kg.
Amorphous silicon is a promising solar cell material. In terms of raw material consumption, there is no bottleneck in the supply of raw materials. In the manufacturing process, for every 1W battery produced, the power consumption of amorphous silicon batteries only accounts for 7% to 8% of crystalline silicon; under the same light conditions, amorphous silicon thin-film batteries The annual power generation capacity of crystalline silicon batteries is increased by about 15%. The power generation capacity of amorphous silicon batteries under low light conditions such as morning and evening, rain and fog is significantly higher than that of crystalline silicon batteries; in terms of application carriers, the base of amorphous silicon thin-film batteries can be The large area of glass, which can also be active plastic or stainless steel, can be integrated with architectural decoration and has a wider range of applications. These provide a broad range of applications for the amorphous silicon thin film battery industry.