We describe this crystalline silicon cells on recent examples. We will look now more closely to performance and operation. We present here the typical characteristics I(V), corresponding to P, optimized silicon cells of 100 square centimeter. The slope at the origins near I on V equal to zero are optimal, which means that there are very few series on parallel resistant effects. The values parameter are shown here. The total thickness of the cell is of a few hundreds microns. In contrast, the A layer very thin, less than one microns so a typical lifetime for the electrons are a few hundred microseconds much less for the holes. Likewise with diffusion lengths is of the order of 500 microns or one millimeter for electrons much less for the holes. The recombination rate at the surfaces is defined by this relationship. Indeed the presence of defects on the surface induces rediffusion current. If the defect density is N def the current will be S def, where S is recombination velocity. S front face is typically of the order of 10 to the 2, to a few 10 to the 4 centimeter per seconds. At the back from 10 to the 2 to 10 to the 7. 10 to the 7 corresponds in fact to the lack of BSF. Therefore, there was typical parameters of a solar cell based on crystalline silicon, slightly better for monocrystalline than multicrystalline. We can simulate the operation of the cell as illustrated elsewhere in the exercise. There follows some parameter influence examples, start with maximum power Pmax, which was defined on the previous slide. Depending on lifetime of electrons in the P region. More silicon is pure the longer the lifetime so more Pmax increases, but beyond 100 microsecond, the effect is saturated. This means that more of the silicon is pure, more the performance will be better. But beyond a certain point, it is no longer very useful to continue to purify silicon so corresponding additional cost does not induce a significant increase in power. Let's move now to the effect of temperature operation of the solar cell in degree key. When the temperature increases, the VOC decreases in blue, on maximum power, in red. It is the same for the efficiency. In practice, this is an important fact because when exposed to the sun, the module temperature naturally increases for various reasons including encapsulation, glass polymer, and so on, which absorbs inside. This effect can be interpreted easily. Location of electron hole pairs by thermal effect increases with temperature according to Katie Bolt Mandl. Take the case of N type silicon. It means that the creation of holes assist with temperature which means that quasi Fermi level decreases to work with the middle of the band gap. So, the VOC which measures the difference between the quasi Fermi level of the N on p zones, will decrease by thermal effect. The congestion efficiency of the crystalline silicon thus decreases as function of temperature. Let us deal now with another effect, the influence of the Rear Contact. I present the VOC on ISC as function of the recombination rate of the rear surface. The IS values of SBSF correspond to the lack of BSF. High surface recombination. The current collection decreases because of the loss of carriers by recombination, decrease of ISC. VOC decreases with SBSF for the same reasons. As the density of carriers in the condition bonds is exponentially dependent on the distance. For example, between EC on EF for our N type semiconductor, the carrier density decreases as the Fermi level moves away from the bond edges. Therefore, VOC decreases. This can be a significant effect, observe here, since such a reduction is a shot weak current is of order of 20%. We will illustrate other effects by using the spectral response which measures the efficiency of the cell as a function of the wavelength. More specifically, the shots of weak current dependent on the wavelength. The right curve corresponds to the cell corresponding to the parameter presented previously with BSF, but without surface passivation. If we add a surface passivation, we find that the efficiency is a blue point for microns increases. In this the blue photons are absorbed near the surface of the silicon, and thus very sensitive to the passivation of the front panel. The second dotted curve correspond to the lack of BSF. The rear face is sensitive to the absorption of photons in the bulk of the material, which corresponds hazard to the inside or head wavelengths. For the BSF improves the collection in the long wavelengths. Let us have in what well the most efficient solar cells on the market. Currently, the world record is held by SunPower a subsidiary of Total, the famous French Oil major. The left figures correspond to the SunPower commercial fly sheet silicon cell and doped. The main originality of the cell is that the contacts are transferred to the backside, for electron on holes with BSF. This cell is clearly based on the diffusion of carrier within the back silicon on selective contacts on the back. Lack of front contacts avoid shedding effects that decrease ISC. However, passivation, particularly of the front face must be excellent. Recent power modules often appear as completely black so are very easy to identify. The performance of this module can exceed 20 or 21 person guaranteed for 20 years operation. These modules are very efficient so they can be coupled with concentration, typically, one dimension so as to reduce the silicon surface exposed to the sun. SunPower sells on the market concentration system of several megawatts. This slide illustrates the operation of a crystalline silicon module in real conditions. These data were recorded in April 2015, on the campus of Ecole Polytechnique, a sunny day. The module is oriented to the South. Power supply by the module changes in irradiance with the maximum, around solar noon. The bottom figure shows the changes in efficiency on performance of the module. April 19th is located approximately one month after the spring equinox. So, the sun rises and sets in the Northeast, that is to say, behind the South on your T module. Under these conditions, the cells convert only diffuse light in the early morning. The produced power is very low, but with a pretty good conduction efficiency, shutting off 14%. Later, the module begins to be sensitive to direct radiation, but at grazing incidence. The yield dropped to 7% due to the optical losses. So the same behavior is observed in the evening. Then the angle of incidence decreases, the power output increases and the efficiency reaches 15% on the module temperature, 21 degrees C. The power delivered continues to increase as the temperature reach 15 degrees at noon. That is to say much more than room temperature. Radiation inefficiency of crystalline silicon module is up-scaled 12.5% effect discussed both. Later in the afternoon the temperature decreases and the yield rises 13.5%. This example show that in real condition, nominal performances are not achieved due to optical losses on silicon heating. Let's finally address the main application in terms of energy pollution. Photovoltaic solar power plant. The figure shows a view of the Cestas plant, in France near Bordeaux, Gironde, open in 2015. It occupies about 260 hectares ground. The P power solar noon AM 1.5 is 300 megawatts. The annual energy production approximately corresponds to the consumption of the city of Bordeaux. Note that your expected cost of energy is significantly lower than that of the EPR nuclear project in England. The largest plant in style in the world is currently in the United States, in California. Its total capacity approaching for 600 megawatt peak. It is equipped with SunPower modules. I have described in the previous sequences the solar cells based on crystalline silicon, monocrystalline, or multicrystalline. Now we will discuss in the final section, sales based on three-five semiconductor, in particular iPerformance multi-junction. Thank you.
