(Chemical Vapor Decomposition)
Photovoltaic solar panels are designed for direct conversion of solar energy into electricity. They consist of a plurality of solar cells (cells) which are made of silicon, one of the most abundant elements on earth. Structurally, the photovoltaic solar module is electrically interconnected solar cells having output terminals for connecting the loads. Each cell contains a semiconductor layer 2: positive and negative. On the silicon layer is applied to one particular substance, whereby an excess of electrons. This forms a negatively charged n-layer. On the other layer created deficiency of electrons and becomes positively charged (p-layer). When a photon of light on the solar cell, the electromotive force is created, which creates the outer loop directional movement of electrons is what we usually call an electric current. Current (amps) is proportional to the light energy (number of photons) and the size of the solar cell. Now solar cells made of different materials using a wide range of technologies and approaches to production. However, the principle of their work, based on the use of the photovoltaic effect (increasing the potential difference in a semiconductor n-p transition under the influence of rays of sunlight) is one. Properly mounted solar array will be a reliable, environmentally friendly source of energy for many years. All solar cells can be divided into two main groups - crystalline silicon and thin film.
Photovoltaic industry today needs to increase the conversion efficiency without compromising the economic and technical aspects of the industrial production.
Chemical Vapor Deposition
CVD is a versatile and economical energy method atomic-molecular coating formation by the controlled deposition of the substance in the form of individual atoms or molecules in order to produce films with the required properties (desired density, thickness, orientation, composition, etc.).
In CVD material is deposited in the form of powder, if the chemical reaction of its particles in the solid state takes place only in the gas phase, and as a film coating, if reaction of the particulate material occurs at the surface of the substrate. It is obvious that for functional layers IC is suitable only the second group of the processes of chemical vapor deposition.
Areas of the gas phase and the substrate surface, in which chemical reactions occur heterogeneous CVD layers can be combined by introducing the concept of "reaction zone." In general, the thickness of the reaction zone is several atomic sizes of the current boundary of the deposited layer.
The reaction proceeds in several stages and, in general, by several routes first route characterized by the steps:
- Formation of the starting reagents A and B in the gas phase of intermediate I;
- The formation of a by-product gas end C.
The second route is characterized by the steps of:
- Formation of the starting reagents A and B in the gas phase of intermediate I;
- Reacting an intermediate I with the surface of the growing layer to form the intermediate R;
- Conversion of the R in the reaction zone in the structural units D of the functional layer and the regeneration element clean surface.
Finally, the third route characterized by the steps:
- Adsorption of reagents A and B;
- Their interaction in the absorption layer to form the intermediate R;
- Conversion of the R in the structural units of the functional layer D.
This is generalized kinetic model of CVD material layer D on the surface of the substrate W by the reaction A + B-> C + D, where A, B - initial reactants, s - surface of the growing layer D; As, Bs - reagents in the adsorbed state on the surface s; I, R - intermediate reaction products in the gas phase and the adsorbed layer on the surface s, respectively; C - end side reaction product gas; 1 reactor 2 - a substrate holder; 3 - the reaction zone; 4 - feeding the starting reactants into the reactor; 5 - removal of the reactants and reaction products from the reactor.
Thus, the functional layer CVD formulated as a problem of chemical kinetics multipath multi-stage reaction. In general terms, this problem has been solved. For the analysis of the specific reactions necessary to know the full set of rate constants of the individual stages, which is an experimental task of great complexity, but its solution can be used approaches of the theory of the kinetics of heterogeneous catalysis.
Production of solar cells (photovoltaic cells) by ink-jet printing is a simple, inexpensive method of coating the surface of the semiconductor material and the electrodes using an ink jet printer. This approach is being developed by various institutions, including the University of New South Wales (University of New South Wales), State University of Oregon (Oregon State University) and MIT (Massachusetts Institute of Technology).
Inkjet printing is one of the newest and most experimental methods used for the production of solar cells, and plays a potentially huge role in the production of public solar panels. The basic principle of inkjet printing is the use of a number of nozzles for the contactless transfer ink directly to paper or other surface (in this case, without touching it). This allows not only printing on a variety of surfaces, but also on various materials.
In general, solar cells are manufactured by applying a semiconductor material and electrodes on any surface using an ink jet printer. Both organic and inorganic solar cells can be produced by ink-jet printing. Organic solar cells printed with inkjet printers are basically CIGS solar cells. Typically, paints are composed of mixtures of metal salts (CIGS) in the case of an inorganic solar cell. CIGS is particularly well suited for forming thin film solar cells because it absorbs light more than the conventional semiconductor that is widely applicable in computer industry - silicone. Thus, CIGS layer 1-2 microns thickness substantially the same capable of effectively absorbing the energy of the photons as the 50 micron layer of silicone.
In the case of organic element, the paint is a mixture of the polymer with the fullerene. Further, the ink is transferred to a variety of surfaces. In most cases, the more the deposition of several layers of other material or member extends other processes to complete processing. The whole process is carried out at atmospheric pressure; Temperature may reach up to 500 ° C. Important factors that should be considered for high performance printing elements are: the time of latency inkjet; the temperature of the printing table; the effect of the chemical properties of the polymer of the donor.
Main advantages of manufacturing solar cells by inkjet printing is low manufacturing cost because of the lack of need for vacuum equipment that makes cheaper. Also, mixtures of metal salts, which are used for paints, reduce cost of solar cells. In comparison with methods such as vapor deposition, an inkjet method generates little waste materials. This is due to the fact that the printer is able to create a very precise structure. Some solar cells, printed ink jet printer is used CIGS material, solar performance efficiency is higher in comparison with the conventional silicon solar panels. Using CIGS makes such a factor as a small amount of waste, more importantly, in view of the rarity of some materials. Moreover, this method is environmentally friendly since it does not require the use of toxic chemicals for production of solar cells, as is the case with other methods.
However, the efficiency of inkjet printed solar cell is too small to be commercially viable. Even in the case of increasing the effectiveness of the materials used can be a problem. Indium - rare material which may disappear in the next 15 years, with the tie in order as used at present. Another problem - is the production of weatherproof paints that are able to survive the harsh conditions.
In conventional solar cells the surface on which the photoelectric material generally costs more than the material itself. With inkjet printing made possible solar cells on paper that will allow the solar cells to become much cheaper and will provide an opportunity to place them almost anywhere. With the presence of paper solar cells will be possible to place them on the curtains, windows, shutters and virtually anywhere in the home. This is a very promising and could become the future of solar energy.
Jaeger, Richard C. (2002). "Film Deposition". Introduction to Microelectronic Fabrication (2nd ed.). Upper Saddle River: Prentice Hall. ISBN 0-201-44494-1.
Smith, Donald (1995). Thin-Film Deposition: Principles and Practice. MacGraw-Hill. ISBN 0-07-058502-4.
Dobkin and Zuraw (2003). Principles of Chemical Vapor Deposition. Kluwer. ISBN 1-4020-1248-9.