[MUSIC] >> Turning now to the study of solar cells made of amorphous silicon and alloys. It is therefore necessary to extend the space charge region as has been seen so that the abstraction of photos takes place in the presence of an electric field, which will separate the carriers. The easy way to extend the region is to use p-i-n structures so that the electric field is present throughout the thickness of the component, as seen here. The p on n zones which have many detects, as thin as possible, just sufficient to establish the internal electric field since they do not significantly contribute to the collection. It may be noted, some technological problems. Since the absorption of blue photons that is very strong in all semiconductors, so will take place is doped areas, as [INAUDIBLE] of the cell. However, it's necessary to have sufficient thickness to absorb all red photons of the order of one micron. But if we increase the thickness of the cell, it will be increasingly difficult to collect generated by blue photons. Nevertheless, Metallic electron being reflective therefore it increases the effective thickness of the cell. We now surmise the physical properties of the p-i-n junctions. The zones content acceptor ions first row's atoms. The eye layer is in which takes place. We will see below that the electric field extends across the component. The intensity of the electric field decreases with the thickness of regions. I remind you that your thin silicone base layers are made from PECBD method, that is to say a dissociation of a gas precursor in your active plasma. For example, saline SIH4 for silicon. But the saline may be mixed with gas giants of the pods, thereby allowing the growth of the end on P layers. Saline can be also mixed with carriers of carbon or germanium such as methane or germane, which makes it possible to vary the gap of the semiconductor from amorphous silicon. It is, for example, narrower by introducing germanium. It is seen here as right, the influence of the introduction of germane on the optical properties. If it is deposited material from pure germane, we obtain hydrogenated amorphous germanium with the band gap of about one eV on the left. Then depending on the saline germane mixture, we can adjust the band gap between 1 and 1.8 eV. Then what we see on the right, If the saline is mixed with methane, we can vary the bond gap between 1.8 to 2.2 eV, about. Thus, one can vary the bond gap of thin film-silicon mixture between 1 and 2.2 eV, which provide a great flexibility. This is an advantage of the plus [INAUDIBLE] processes that can, as we have seen, be extended in large area because of the capacity coupling with planar geometry. I should however add a note, this alloy's are hydrogenated, so the material is internally hydrogen, silicon, germanium or silicon, carbon, hydrogen. Internally materials preservation by hydrogen is not as optimal as in amorphous silicon. Because of the different chemical affinities of hydrogen with silicon and germanium, for instance. In fact, in photo voltaic applications, only the low carbon or germanium alloys are used. And also, a way to vary optical properties of silicon layers is to vary the crystallinity of partially other materials. Here, we see in this figure, the influence of crystalline production in silicone. The [INAUDIBLE] corresponds to hydrogen and [INAUDIBLE] silicon. When the crystalline volume [INAUDIBLE] increases, when it gets optical properties close to crystalline silicon. We have a threshold of about 40%. That is to say therefore, gap on small band gap blue curves. As previously mentioned, it is advantageous to decrease the optical absorption of the window layers. This can be achieved by using your higher band gap material such as silicon carbon as generally done in practical applications. Nano micro silicon with optical properties close to crystalline silicon can also be used as a window layer as seen in this figure. I show on the left the diagram of a. I show on the left the diagram of a solar cell made from high version silicon, the photon flux coming from the left. The deposition is made on the glass substrate cover with a thin layer of oxide transparent conductive oxide electrode. This in appendix one. Window is made of silicon carbon then the cell consists of amorphous layers. The presence of layers improves the quality of the interfaces. A display on the right is stability film layer. That is to say the relative evolution of the conduction efficiency, depending on the time of exposure to the sunlight. Polyamorphous silicon cell, in red, degrades very little upon exposure to sunlight. In contrast, in the case of hydrogenated amorphous silicon in black. There is another of loss, inefficiency of 25%. After a week of exposure, this comparison illustrates the advantage of using partially order thin layers. Certainly, by alleviating, it is possible to return to the initial conditions in the case of hydrogenated amorphous silicon but is not possible in the case of modules in cell in roofs. I show you here an example of a single cell on small area, 0.25 square centimeter, that was prepared at the corporate in LPICM. The view you see exceed 0.9 volts, which is much higher than that of crystalline cells. So fill factor, which is on the order of 0.7 on the stabilized efficiency of the order of 9%. So transparent conductive oxide layers are used either as an electrode either for optical optimization index matching or for both. It can get slightly better efficiencies with a nano or micro crystalline silicon thin film, as seen here. These is an optimized cells on small layer made in Germany in the Fraunhofer Institute. The thickness of the layer is higher for the nanocrystalline silicon because it absorb less than the normal form of silicon. Under optimum conditions, one can obtain slightly higher efficiencies of 10% for partially crystallized thin silicon cells. What are the general trends for the thin film cells technologies? PECVD has great potential because it allows the deposition of hydrogenated or partially crystallized amorphous silicon, as well as alloys, by changing the condition of the plasma. Typical stabilized conversion efficiencies are in the range of 8% to 10%. The major disadvantage of hydrogenated amorphous silicon is linked to instability phenomena on the relatively low deposition rate. It typically requires a [INAUDIBLE] of the order of a quarter [INAUDIBLE] or [INAUDIBLE] to prepare a cell of micron thick. So polymorphous silicon has optical properties similar to those of a amophous silicon. Compared to the amorphous silicon, it has advantage of the i deposition right, since the from crystallize on the better stabilities I would have seen. But the nano or micro crystalline silicon, according to the crystallized volume fraction, has optical properties similar to crystalline silicon, and furthermore, better stability. It appears as a complementary with amorphous silicon. This is what we will see in the next sequence. We thought the thin film solar cells based on silicon. We will focus thereafter on the mixed cell, that is to say the multi junctions which include different materials. All thin film cells use transparent conducting oxide. They are described in appendix 1. I advise you to have a look to this appendix. Thank you. [MUSIC]
