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Preparation and characterization of nanocrystalline silicon thin film solar cells

Core: with the acceleration of industrialization and urbanization, the traditional energy resources such as minerals are becoming more and more scarce, which can not meet the needs of people's life and production. Therefore, renewable energy attracts more and more attention. As solar energy is an inexhaustible, clean and pollution-free energy source, governments around the world have studied and developed the sun

With the acceleration of industrialization and urbanization, the traditional energy sources, such as minerals, are becoming more and more scarce, which can not meet the needs of people's life and production. Therefore, renewable energy sources are attracting more and more attention. Because the solar energy is an inexhaustible, clean energy, governments around the world to the research and development of solar energy as a strategic decision of energy sustainable development in developing countries, developed countries such as USA and Japan and Chinese were made of photovoltaic technology development plan, the photovoltaic power generation as the energy of human hope for the future. Since the 1954 Baer lab in the United States has prepared first 6% silicon solar cells and 70 Middle East oil crisis in twentieth Century, the research of silicon solar cells has entered an era of great concern.

Single and multi crystalline silicon solar battery photoelectric conversion efficiency is high, they were 24.7% and 20.3% in the highest conversion efficiency of the laboratory, although their efficiency is high, but the raw materials of single and multi crystal silicon complex preparation process and high cost, the absorption of solar spectrum, theoretically only crystal wafer thickness is about 100m, far below the thickness of about 180pm battery current industrialization, resulting in unnecessary waste, based on cost considerations, people thought of the preparation of low price and simple process of the thin film solar cell, the utility model has the advantages of raw materials and finished in the battery experiment instruments at the same time, unlike the crystal silicon battery requires two links, namely the battery preparation and crystal silicon raw material of a silicon wafer for preparation of the two process, which greatly saves raw materials and labor costs. At present, there are 3 types of silicon-based thin-film solar cells: microcrystalline silicon thin film solar cells, amorphous silicon thin film solar cells and nano silicon thin film solar cells.

The preparation, has the advantages of silicon thin film solar cells in a preparation process is simple and convenient for large area continuous production, is an indirect band gap semiconductor material, high stability, less than the amorphous silicon absorption coefficient in the visible light, which means that the same sun light absorption, H of microcrystalline silicon raw materials needed if not, H will be passivated, blocking effect of crystal boundary 0. which contains the advantages of amorphous silicon electronic transmission capacity, no light attenuation effect, more sensitive to red spectral response, increased from amorphous silicon 700nm to microcrystalline silicon 1100nm1,. The amorphous silicon thin film solar cell by Carlson and Wronski in 1976 for the first time preparation, non crystalline silicon thin film optical absorption coefficient, absorption coefficient of small compared with other film absorbs the same sun and saves more raw materials, the use of cheap substrate materials such as glass, stainless steel and plastics, simple preparation process, can achieve a large area and continuous production, reduce the cost; but the non crystalline silicon thin film light attenuation effect (Staebler~Wronski) H, the deposition rate is slow, affecting 5. large-scale production of nanometer silicon thin film for the first time by the Veprek group reported in 1986 since 63, both at home and abroad for the nanometer silicon thin film battery materials, preparation and property study has made great progress. With nanometer thin film materials of high conductivity, low activation energy, thermal stability, light absorption ability, can reduce the optical gap width, simple preparation process, quantum size effect etc. 673. when the crystal size to the nanometer scale, due to the large surface volume ratio, its physical properties different from bulk materials, for the bulk properties of atoms within the decision of material, nano materials and surface atoms determines the properties of the material 8. degrees so the physical and chemical properties of the nano thin film solar cells will have a strange effect. At present, a large number of domestic and international scientists are investing in the research of nano silicon thin film solar cells. For example, the preparation methods of plasma enhanced chemical vapor deposition of heterojunction solar cells and the influence of external conditions on the optical and electrical properties of heterojunction solar cells are described in detail. But there is little research on like amorphous and microcrystalline silicon solar cells, the general physical mechanism of thin film solar cell photoelectric conversion efficiency theory and the effect of preparation comprehensively nanometer silicon thin film solar cell, so the research on this system is of great scientific significance.

Preparation method and deposition theory of 1.1 preparation methods of nano film 1 nano silicon thin film solar cell: plasma enhanced chemical 61, hot filament chemical vapor deposition (see HotWire deposition in a plasma enhanced chemical vapor deposition.

Plasma enhanced chemical vapor deposition of reaction gas through the RF electric field generating a glow discharge plasma formation, in order to enhance the chemical reaction, thereby reducing the reaction temperature, a new growth method of silicon nitride, silicon oxide, amorphous silicon, nano silicon and phosphorus silicon glass semiconductor device surface protective film at low temperature.

1.2 sedimentary theory and nucleation theory, the thermodynamic reaction equation as follows: the growth of silicon nano films with high hydrogen dilution of SiH4 M: the forward and reverse reaction rate, the film deposition process for gas phase and solid phase is the inverse process of reverse chemical reaction is called corrosion process. This process is the process of damaging the weak Si-Si bonds produced by the H group in the plasma. The thickness and quality of the nano thin films are mainly determined by the 2 reaction processes.

When the gaseous SiHx encountered the substrate, the substrate surface will be in transport, if appropriate lattice, in which silicon grains will accumulate and form Si-Si bond, along with the continuous reaction, silicon crystal nucleus will continue to grow, if in the process of nucleation, weak Si-Si bond, H base this will erode the bonding state, until the stop, after such a series of silicon nanocrystals formed M. 2H dilution effect on the properties of nano silicon thin film solar cell silicon nano film usually by H2 and the ratio of SiH4 to prepare, it can passivate the dangling bonds, have corrosion effect on the film, H concentration is an important parameter in crystalline silicon thin film and solar cell performance. For example, 14 of the intrinsic layer of hydrogen dilution ratio SH=H2/ (H2+SiH4+PH3), and the performance parameters of solar cell, the article points out, with the increase of hydrogen dilution buffer layer, the open circuit voltage of solar battery is reduced, the short-circuit current increases rapidly, but when about Sh>97%, short circuit current decreases rapidly; filling factor increasing obviously, the battery efficiency increased, but at about Sh>97%, there is a sudden decrease. They think the reason may be to increase the hydrogen dilution buffer layer, doping efficiency, the Fermi level increased, but the gap width decreases, both comprehensive effect to reduce the open circuit voltage; the increase of the hydrogen dilution, grain size and the increase in carrier mobility, improve the electrode on the carrier collection, improve the short circuit current. But excessive dilution of H, increase the corrosion, forming defects, composite, reduce short-circuit current. 9, similar conclusions have been drawn. 14 also studied the relationship between different i layer, H dilution and quantum efficiency of solar cell, the article points out that with the increase of hydrogen dilution, short wave absorption increases, the short-circuit current increases, this conclusion with the above conclusion, such as mutual unification.

3 Effects of deposition pressure on the properties of the film properties of the film, with the increase of the deposition pressure, silicon nano film crystallinity increased, such as changes in Table 1 and the XRD 3 peak position strength you can know. This conclusion is consistent with the 7 Raman spectrum test results, such as.

4 Effect of substrate temperature on the properties of the film pressure parameter sample working pressure in Table 1 of the /Pa films, as shown in table 2. the article pointed out that, with the increase of substrate temperature, film band gap width decreases, the hydrogen content increased, increasing the dark conductivity and photoconductivity. This material can be applied to the intrinsic absorption layer of thin film solar cells.

Table 2 transparent conductive film and nano silicon photoelectric properties of hydrogenated amorphous silicon materials common bandwidth of 5 RF power density /mW /Torr substrate temperature / pressure especially 5 transparent conductive film in nano battery application in thin film solar cells, has a low resistivity with light transmission and has the environmental stability the characteristics of high visible light. These materials include indium doped tin oxide (ITO), indium doped Zinc Oxide (IZO), aluminium doped Zinc Oxide (AZO), tin oxide doped with fluorine (FTO), antimony doped tin oxide (ATO) and so on.

For the conventional transparent conductive film (TCO) such as: ITO, AZO free carrier absorption in the near infrared region, limiting the nano silicon solar cell long wavelength response M, recently some scholars have studied the molybdenum doped indium oxide applied in thin film solar cells (IMO) transparent conductive film. Having better optical properties, such as.

ITO and IMO films can be seen from the comparison of the transmission spectrum, compared with the general ITO transparent conductive film, IMO film has wide transmission band, ITO after 1750nm and the band almost no light, while the IMO film has high transmittance, good optical properties. Nano silicon solar cell with this film made of such good quantum efficiency 6.6 summary this paper reviews the development history of solar battery, expounds the nature and characteristics of single crystal silicon, polycrystalline silicon battery, microcrystalline silicon solar cells, thin film solar cell; enhanced chemical vapor deposition and preparation of nanometer silicon thin film deposited by plasma theory. Solar cells are described; demonstrates the effects of H dilution concentration on the performance of solar cell silicon nano film, with the increase of hydrogen dilution buffer layer, the open circuit voltage of solar battery is reduced, the short-circuit current increases rapidly; describes the influence of deposition pressure and substrate temperature on the properties of the films, the deposition pressure increases, silicon nano crystal film the degree of increasing substrate temperature increased, film band gap width decreases, increasing the dark conductivity and photoconductivity; finally The applications and optical properties of transparent conducting films in thin film solar cells are investigated. The influence of deposition conditions on the properties of the films is still under further investigation.