 Good morning everybody. Today I will be presenting how to work on this PC1D simulation. So, it is basically simulation software published by the University of New South Wales and it is it basically works on one dimensional transport of electron and holes. And so there is a nothing like two dimensional transport like as we can specify the finger spacing on the top surface or anything else within the device. So, it basically takes the whole region as one dimension although it shows the overall this is a cross sectional view of the device. So, as we progress in designing the cell we will see how it is happening, but the whole thing happens in one dimension way in the z direction or kind of depth wise. So, e is the emitter part and b is the base part. So, the dimension starts from z dimension z o is at the emitter level I mean at the top surface and base is the rear surface. So, if you open this file you will find different parameters to be set here to design the device. So, the first thing is like what is the device area. So, that will be the top surface where the irradiation is falling. So, we can put it like say if you double click on this parameter you can put the value of the top surface area. So, we can put it like 100 centimeter square let us say. So, generally for 125 by 125 centimeter square cell you can put 156.25, but here we are putting 100 centimeters for our calculation it will be easier. On the device area double click on the device area on this point. Again all these points will be available on this menu bar. So, if you click on the device you will you can also put the area from here. So, every option listed here will be available from this menu. So, next point is the surface texture. So, if you click on this texture you will get an default value of 54.74 degree. So, this is some kind of assuming some facet model it takes this is the angle between 111 and 100 plane. So, this things should remain the same I hope and depth you can change according to your model. I mean if you want to have some deeper surface texture then you can change. Let us put it like 3 micrometer only. Yeah the texture height at the surface. Yes please. 100 plane see 100 is the plane in which atomic density is very high. So, when you know how the texturing is done. So, yeah that is the texture pattern, but how is it done is that you put the wafer in a KOH or TMAH solution where the KOH this KOH or TMAH solution attack the silicon atoms. Now, the 100 direction the is the depth wise direction in which the etching of the atom will be very fast. So, it will be very deep enough, but the 111 plane will be very slow. So, it will create a pyramid on the surface. So, that angle is here specified by this 54.74. Now, the third point is the surface charge. This is basically I think everybody is fine with the surface texture. So, third thing is that this surface charge this is basically important in the other kind of semiconductor devices where suppose you grow a silicon. Yes please. It will be the flat plane surface. If you look at this let us say see if you select this texture you can see on the surface it shows the texture kind of thing. If you do not select this texture it will be kind of plane surface. So, it will not take the texturing thing and the reflectance and other things it will not be there. Yeah, texture. No, it is basically it is taking only the pyramid structure. You can also go in practice you can also the go for the inverted pyramid like kind of thing or these are kind of smooth I mean uniform pyramid heights at every distance, but in actual solar cell we do not go for this smooth kind of thing. In actual solar cell it forms a random pyramid structure, but those things are not taken into this software. So, this is kind of very basic thing for that is why we are taking it is taking only the uniform texture height at every point of the surface. Can itself be arranged here to go even here? What you are talking about exactly you are not getting. Okay. So, if it can be arranged physically here and it is shown and point out there. Okay. Yeah, I can arrange one thing, but I can arrange the cell that is not a problem, but only thing is that you cannot be able to see the textures because it is 3 micrometers. So, you will see a plane surface that is all. So, I am arranging a cell. So, let me finish it and I will arrange a cell then we will. Yeah, yeah, sure, sure, sure, obviously. Okay. The next thing is the front surface charge. So, this is the charge accumulation on the top surface. So, this is basically important in other kind of semiconductor devices like where you are suppose growing some silicon dioxide on the top and due to the difference in the solubility of the dopant atoms in silicon and silicon dioxide, there is a charge accumulation at the top surface. If you say some values put some values like 20 like thing, some orbit value I am putting. So, it will show the charge accumulation on the top surface. So, but in this case it is not important since we are growing some kind of not growing some silicon dioxide on the top surface. Now the reflectance, reflectance from the top surface. Here you can put either fixed values or some coating you can specify. So, fixed values means you can put a fixed reflectance around all wavelength on the spectrum. See spectrum for silicon solar cell is from 300 to around 1100 nanometer, but for every wavelength the reflectance is different. But here if you put say 10 percent or 12 percent then you will take 10 percent reflectance for every wavelength from the surface. So, this is one thing and the other thing is that the coated thing. So, here you are assuming that it has a basic reflectance and on all wavelength which is around say 10 percent again. Now apart from that reflectance you are putting some layer some silicon nitride layer or anti reflection coating layer to minimize the reflection at a particular wavelength. Like in case of irradiation spectrum the most important part is around 550 nanometer. So, you would like to minimize the 550 nanometer wavelength the reflection of the 550 nanometer wavelength. So, there is a formula called I mean there is a formula through which you can calculate what should be the thickness of the anti reflection coating for a particular wavelength. So, you can put the refractive index of the coating and you can put the thickness. So, by managing these two you can use the minimize the reflection of the particular wavelength. Here is the help menu if you are not understanding you can use that I think is it. Yeah actually the OSS OS is either Vista or Windows 7 I think in ways Vista and Windows 7 the help menu does not work actually. In XP it works there is some file missing for this software. So, that does not work actually. No it does not the help is not it is XP there, but still but still you are not getting the help menu. So, for every point there is a help option available. So, you can go through it if you are not understanding my words you can get references from there. So, the reflectance part is basically again for these two things either fixed and coated. So, you can go for the fixed reflectance lead 10 percent or you can go for a coated sample I mean with some silicon nitride coating. The refractive index for silicon nitride is around 2.0 or 2.1 like that. So, we can put let us say 2.1 and the thickness of the layer is around 17 nanometer. So, and the broadband reflectance we can put again 10 percent. So, both the way you can do it I mean is it fine. See when we grow the SiO 2 it is grown from the top surface. Now, the top surface is diffused SiO 2 grow growth is done after the diffusion process. So, whatever dopant material is down there on the top surface while the growth process it will also be incorporated inside the SiO 2. Now, the solubility of that dopant atom in SiO 2 and silicon will might be different. Due to that difference there might be some charge accumulation at the source surface interface silicon and silicon dioxide. So, that thing can be taken around here. No, that is not for solar cell actually because in case of solar cell we generally deposit silicon nitride. So, that growth mechanism is not very important. Then the next thing is exterior reflectance. This thing you can again put the same thing, but rear reflectance is not generally counted because it is mainly in case of concentrated solar cell where the radiation also comes from the backside. So, this is not important for plain solar cell. This internal reflectance. So, it is due at the interface. So, see if you go for the solar cell you have the cell and on top of it you have the anti reflection coating. So, whatever radiation falls on it on the anti reflection coating first it will get reflected. The less part will be transmitted into the cell. Then at the nitride silicon nitride and silicon interface there will be another reflection. Those reflections are taken account in this thing this internal reflectance and other things. So, you can put some values here say 90 percent and frankly speaking I have not understood this thing actually. So, I am just putting some standard value they have used for PV cell. So, here they are saying reflectance, but they are putting 90 percent, 70 percent like that. So, I think we will put some stand value which they have used in case of solar cell. Then next is emitter contacts. So, here you can put the resistance provided by the emitter contact and the base contact. The position of the contact again can be specified at this point. So, as I said the dimension starts from the front side. So, the emitter contact will be at 0 micrometer and the base contact will be at the position where the at the thickness value will be the same as the thickness. So, still now we have not specified the thickness, but we are putting let us put it like 10000 micrometer that will not be a problem I will explain after fixing the thickness thing and the resistance value you can put accordingly. So, let us put 0.001 and the collector circuit is not important because we are only dealing with the diode structure. So, in case of transistor simulation you might be using this collector that is one thing and so emitter and base contacts are enabled here and internal shunt elements here in solar cell you will find lot of points which is called shunt points shunt path or shunt points. So, at the previous setting. So, it is kind 0.1 milli ohm and 0.4 milli ohm. So, the shunt things there are two majorly two types of shunt in solar cell one is conductor kind of shunt that is kind of omissions and the other one is directions. So, you can there are four shunt I mean four thing you can specify separately suppose we enable the shunt thing and put a see in case of conductor you have to put the Siemens value that conductance value. So, let us say a shunt is around 200 ohms or 2000 200 ohms let us say. So, 1 by 200 is like 0.05 I think I guess 0.05. So, it enables one shunt path for the cell it will be it will appear here and if you go for the other kind of shunts you can again enable the multiple kind of shunts for the cell. So, that you have to look what kind of shunts is there in the cell you have to model here shunt is kind of see. So, let us say this is N plus p cell solar cell and on top of it you are putting the front contact and do the annealing thing for making good ohmic contact to the cell, but due to some reason suppose this N plus p is done by diffusion. Now, during the diffusion you have some impurity on top of it on top of the surface and you did not get such a uniform junction. So, your junction is like this it is not very uniform over the surface and now you are putting your metal contacts here and doing the annealing thing. So, the metal contacts is penetrating the junction and is again connecting the p type layer. So, these contacts are for N type contacts and for back contacts you have another contacts for p type. Now, you have both the contacts for p type the front one as well as back one. So, it is creating shunt shunt path for the cell. So, it will reduce the effectiveness of the cell I mean there are lot of other things. So, you can put the shunt values in this. So, now the cell thickness generally it is around 275 or 300 micrometer. So, put it 300 micrometer. Now, again I am going back to this contact thing. So, you see here we have specified 10000 the actual cell thickness is 300 micrometer only. So, you can put it 300 here, but if you put values higher than that it will automatically take that cell thickness value as the position of the base contact. Now, the material what material we are going to use. So, if you double click it it will open the set of files for the material. So, you can select this silicon dot Si dot material as the material for the solar cell. So, if you select this silicon material it will automatically take all these models like carrier mobilities, dielectric constant, band gap, inducing condense concentration, refractive index, absorption, free carrier and p type no up to this free carrier absorption. So, it will take the default values from silicon for the silicon. If you just double click on it it will open the material files you select the silicon one you can use also the other things like indium phosphide and germanium gallium oxide other things is it fine. So, if you select this silicon dot matte then it will select all these values the next thing is the diffusion thing how do you diffuse. So, let us take p type background doping concentration as 1.1 into 10 to the power 16 and let us take it p type sorry. So, we are working on this n plus p type of cell. So, let us put this thing is 1.2 to the power 16 it is set already I think. So, this is the background substrate doping thing. Now, you diffuse the front emitter from the front side. So, click on this front diffusion there are lot of options available. So, first enable it now the doping material will be n type. So, now there are different options what kind of profile you want to get basically uniform profile is basically for the ion implantation thing exponential I do not know frankly Gaussian is for two step diffusion and error function is for single step diffusion. So, you can select this any of this thing and here is you have the peak doping which occurs at the top surface and the depth factor is basically not very understood but we assume that it is the diffusion length of the dopant atoms. So, if you select these two automatically you will find the sheet resistance and junction depth accordingly. Suppose it is 1.1 e to the power 20 and let us assume it is to be 0.1. So, it will automatically take the sheet resistance value and the junction depth to be 128 ohms per square and 275 micrometer. If you go for Gaussian it will change accordingly. So, junction will be around 300 nanometer and the sheet resistance will be like 86. So, basically this is the depth thing this is say depth and this is your impurity concentration. So, basically the impurity profile for n type is something like this. So, let us say it is 10 to the power 20 and this is 10 to the power 16. So, the n type profile this is for n type phosphorous profile let us say this profile will be like this for after diffusion thing and your background dopant concentration is constant. So, it is like 10 to the power 16. So, this one is the background doping concentration and this one is the concentration of the n type thing this is p type. So, what of the concentration n type and p type are meeting to same values that is the junction. So, this is the junction depth and this is the p concentration at the surface. So, let me draw the whole solar cell structure and what are the parameters that you need to fill in this. So, the starting material always is some wafer which can be p type ok. So, when you start a wafer let us say it is a p type then you need to give some material parameter. So, if it is silicon then what is it doping level that is the one parameter that you require for the substrate. So, you have to choose whether it is p type or n type that you can do in the simulator and then you have to choose what is the doping level. So, what is the what is the p type then what is the acceptor carrier concentration or what is the doping basically. So, this is one pair this is two choices you have to make while selecting the substrate right. Now, after you make the substrate after you choose the substrate and typically this doping level as we have discussed is about 10 for 16 10 for 15, 10 for 16 it should not be 10 for 12 or 13 or it should not be 10 for 18, 19 it is too high 10 for 12 and 13 is too low doping level. So, 15 and 16 is optimized value, but of course, when you are doing simulation you can try anything and you will find there is the effect of what happens if you choose different ok. The next step in the in the industrial process is actually do the texturing texturing. So, now when you do the texturing it can the whole the wafer then this wafer will become actually like this. Now, the I think the software gives the choice to have the texture surface both front and back. So, you can choose texturing and then there is a parameter to define how much is the texturing. Texturing is done to reduce the reflection process right as a solar cell should be doing three functions absorb as much as possible and separate carriers and collect carriers. So, to increase absorption you need to reduce the reflection which can be reduced by the reflection by the texturing. So, the software will give choice to select the parameter what gives in terms of what height of the parameter is an angle. So, this if you actually zoom into this part of the texturing it is normally a kind of paramedical structure and that is what actually happens in ceiling and also when you do the chemical texturing and if you start the appropriate orientation of the substrate you will actually get the parameter. So, you can choose what is the height of the parameter what is the angle of the parameter. So, that will define your texture surface. So, that is another choice you need to another parameter that you need to make. Now, once you have done the texturing the next step is actually to make the junction. So, suppose this is your what are the choices you already made by this point you already made what is your base which is p type or n type you already decided what is it is toping level you decided whether the front surface is textured or not if it is textured you decided already what is height of pyramid what is angle of pyramid. You already decided what is the bake surface textured or not if it is textured what is the height of pyramid and what is the angle of it. So, that information you given to the software the next step is to make the junction. So, if you are starting substrate is p type of course, your junction doping has to be of opposite type n type. So, then and the pyramid heights are normally in the range of 4 to 5 micron, but your junction depth is very small as I told you the junction depth are typically 300 400 nanometer 500 nanometer what is it mean your junction will exactly follow your top surface like this because this pyramids are very very large as compared to the depth of the junction. And this junction this region is going to be of n type this is going to be of n type one thing second thing the doping of the n type that emitter is much higher than the base doping typically doping of base is 10 for 16 the doping of emitter is 10 for 19 or so. Second thing it is made out of the diffusion. So, the base doping is normally. So, if I look at the base doping it is constant over the depth of the thickness if I look at the emitter doping it is not constant it is certain profile. Now, this profile can be of different type it can be like if you are depends on how you are making the junction. So, are you doing implantation are you doing diffusion if you are doing diffusion it is a one step or two step and things like. So, the profile can be separate and the software gives you possibility to choose one. So, error function complementary is a one function which is normally used or Gaussian one of the two. So, this profile you have to choose Gaussian profile or error function complementary profile and you have to it also gives opportunity to give to choose surface concentration. So, you need to choose this concentration level and you need to choose what depth junction is formed. So, if this is your profile and this is your background doping. So, and this is your surface and this is the depth. So, at this point this is your junction depth the point at which the p type impurity p type doping becomes the base doping n type doping becomes equal to the base doping that is your junction and the both impurities levels are both doping levels are equal. So, now the software gives you opportunity to choose a depth of the junction and the surface concentration. This concentration typically you should choose in the range of 10. So, 19 and the depth now of course, we have earlier solar cell we used to have a in 1960s and also solar cell used to have a junction of 2 micron also, but now it has come down to 300 nanometer 400 500 nanometer and there are reasons there are technical reasons for that and we did not have enough time to discuss in December we discuss everything y 300 nanometer y. So, y surface doping up to this for 19 y the emitter doping is higher than the base doping all those things there are reasons behind that and we will discuss y, but it is not enough time. So, but it gives allow it does allow you to choose the appropriate junction depth which can be up to 300 to 500 nanometer with appropriate profile of the this one can be error function can be Gaussian nobody does the implantation for the junction making this is normally diffusion. So, that is another choice you have to make. So, once you decide this now your emitter is there your base is there what is the next what if we should do the next what else is required to make the solar cell complete putting the context right front and the back context, but one more step we need to do before that is to put the as I said there are two ways to reduce the reflection one is doing the physical modification of the surface that is structuring and other is putting the anti-reflective coating. So, again you need to put anti-reflective coating and you need to you need to define what is that anti-reflective coating it is basically one dielectric material having certain reflective index and thickness and the material. So, you need to so what happens you need to put I am putting a black line here. So, this what you have to put is A R C anti-reflective coating typically anti-reflective coating because light is coming through the anti-reflective coating it should not absorb anything it should be thin right because you want light to go into the solar cell light should not get absorbed into anti-reflective coating. So, typically it should be thin. So, you need to give following parameters one is you need to give thickness you need to give what material it is and also refractive index and refractive index of the layer or you can define the reflectance etcetera yeah the material you defined. So, once you define material you are already defining R I refractive index. So, typical thickness for example, typical material that is used for solar cell is silicon nitride. So, Si 3 and 4 is the 1 minus x Si n 1 minus x. So, this is the typical material, but you can also use silicon oxide silicon nitride silicon oxide there can be several other possibilities of choosing a material. So, once you decide material you already decided the refractive index then you have to decide the thickness of the material. In industry the thickness is in the range of about 17 nanometers. So, your solar cell technology is actually a nanotechnology right according to the definition anything below 100 nanometers in nano. So, solar cell commercial solar cell do make use of nanotechnology 17 nanometers then you can actually define the reflectance overall reflectances as well how much should be the reflectance 90 percent 80 percent how much it should be very low not in 18 90 percent if 18 90 even nothing will work right ideal it should be 0 and practically 0 is not possible. So, it will be like in the base cases people have demonstrated up to 3 4 percent overall reflectance across the all wavelength that you can define. So, it can be 3 4 5 10 percent depending on the what else you can define in terms of ARC. So, yeah that. So, R I you can refractive index you can choose. So, if you look at the reflectance profile if you will if you choose single layer inter reflective coating the reflectance profile looks like this. So, the minimum. So, this is the reflectance and this is the wavelength. So, minimum reflectance will occur at one wavelength right, but you want to minimize the reflectance at several wavelength. So, then people actually can come up with the double layer inter reflective coating where there will be 2 with minima reflectance or you can choose 3 of them, but as your I mean as you are putting the more number of layers in practice it becomes more and more difficult to make such device and also the thickness will increase absorption in the inter reflective coating will increase which is not desirable. So, industrial solar cell only make use of single layer inter reflective coating that is the ARC, but in when you are doing your laboratory solar cells and you want to maximize your efficiency you can go for double layer also. So, there is another choice that you have to make and then BSS is very. I do not know. So, now, so your starting substrate was P your emitter is because heavily doped when doping is higher then we add plus sign. So, it is called N plus if there is even higher doping we call it N plus plus. So, depending on that. Now, what people actually do is which actually occurs automatically in industrial process is to reduce the recombination of the back surface they create some kind of field at the back side and they call it back surface field. How does it work? So, how do you make back surface field? Let me put it here. So, they make a P plus heavy doping of the boron. So, how does it work? So, you have again and this region is a P plus region. So, what is the solar cell structure not P N anymore it is a P plus P N plus that is your solar cell. What is the role of P plus? Let us let us draw the energy band diagram. So, if you if you make the Fermi level and this is your P and if it is P plus Fermi level will be closer to the valence band. So, this is your P plus. So, you have such kind of what you see here as soon as you notice this line what do you see? Electric field. Electric field lines are not flat anymore because there is a difference in the doping. So, this is your P plus part and this is your P plus part as soon as you see that lines are not straight or flat which means there is electric field. If there is electric field what does it mean? If there is a electron here it will not go there. There is a problem because it has to go to higher energy. So, it is actually repelling electrons towards this side which is the junction side. So, thus creation of P plus P will create some kind of field which is here and this field will repel electrons towards the junction and we want all the generated carriers to go to the junction. So, that they can be separated and contribute to the current. So, that is why this backside field is important very important for the operation and it is referred as the B back surface field. So, you can again define the back surface field. What are the parameters you think will be there for the back surface field? Doping of course, P plus doping. So, if base is P, P plus will be higher. So, if base is 10 for 16 your B S F will have higher doping for 18, 19 and again the thickness of the B S F layer typically 4, 5 micron, 10 micron that you can have. So, the parameter that you need to do is doping and the thickness doping in this case would be about other tens power 18, 19 per centimeter cube and thickness can go from few microns to tens of 10 micron let us say 2 to 10 micron. What else? So, once you decide once you. So, bulk means basically the base material which is the bulk of the material. Another parameter for the base material is one parameter is doping that is doping wafer, but other important parameter is the lifetime. Lifetime is the lifetime of the carriers. How long carriers remain in excited state before they recombine? Higher the lifetime better it is. So, lifetime can vary from very bad material which will have lifetime of nanoseconds to good material, very good material which will have lifetime of milliseconds. So, several orders of magnitude it can vary which is very very important. The very high quality material like float zone silicon will have very high lifetime milliseconds, but it is very expensive. Nobody use those kind of material for making commercial solar cells. Very low lifetime like nanosecond which is the case for very degraded material like amorphous silicon which is extremely bad and crystalline silicon lifetime is better than that. So, crystalline silicon solar cell monocrystalline particularly will have lifetime in the range of microsecond. Typically it will go from let us say one few microsecond to 20, 30, 100 microsecond. So, that is the typical range of the lifetime. So, that you have to define for your base material. So, what I am saying is for crystalline silicon this can go from few microsecond to let us say one microsecond to hundreds of microsecond. So, that is the range that you have to define. By defining the lifetime what are you doing? You are defining the quality of the material right. By defining the lifetime you are defining the quality of the material. So, higher quality material will have higher lifetime which means carriers will remain higher spend higher time in the excitation mode. Then we before before coming to the context there are there are now you are. So, at end you have to make a context and of course, front contact probably you have to define the finger between everything. You cannot define and the back contact in the crystalline silicon solar cell is continuous. So, back contact is continuous, front contact is not continuous. Why? Because you need light to get in right. You cannot make a continuous contact if you put metal everywhere nothing will go in. You need to give a space for the light to go in. Now, once carriers are there they can actually recombine at three places they can recombine in the bulk of material. They can recombine in the surface which is the front side and they can recombine at the back side. And the recombination something we all want right. We do not want oh sorry. So, recombination something we do not want right. We do not want anywhere the recombination. So, we need to tell this the simulator that what is how much is the recombination taking place? How much is the recombination taking place? The recombination in the bulk has already been defined by the lifetime right. What I am saying? Lifetime is 10 microsecond which means carrier will not recombine up to 10 microsecond after that they will recombine. So, you have already defined it, but the recombination at the surface is surface itself is a two dimensional structure right. The bulk of the material is a three dimensional surface is a two dimensional. So, at the surface recombination is defined by not lifetime, but it is defined by what is called surface recombination velocity ok. Surface recombination velocity ok. It is a rate of recombination per unit area at the surface. So, the unit of surface recombination velocity will be what? What will the unit of surface recombination velocity? It is a velocity right. So, it is a centimeter per second ok. Higher the velocity higher the velocity better it is or worse it is? Worse it is right. Higher recombination velocity means lot of recombination taking place. So, we do not want higher recombination velocity ideally, but naturally that is that does not happen. So, high value of surface recombination velocity which is really really bad is stands for 6 centimeter per second extremely high recombination ok. A moderate value of surface recombination velocity is stands for 3. Or of that order and a very good value of surface recombination velocity is 10 ok. 10 is very good this is moderate and this is very bad ok. So, by doing the deciding the surface recombination velocity we are defining how much is the recombination taking place at the surface. Is the recombination at the surface is in our control? Is the recombination at the surface is in our control? Yes, we can control it by appropriate treatment of the surface ok. So, for example, your anti-reflective coating silicon nitride is not only anti-reflective coating, but is also a passivational layer or control layer which reduces the recombination, but not extremely effective. There are other ways of doing. So, your normal silicon nitride layer will give recombination to that level a survey at 10, 4, 3 at that kind of level, but you can do much better than that. But remember in practice there is always cost associated of doing things better you know you can start with extremely high lifetime material, but it is expensive you can do the very nice texturing it is expensive you can do very nice anti-reflective coating, but it is expensive you can do very nice surface specification, but expensive. So, there is always you need to look at the compromise between the material parameter or the technology that you choose and eventually what you get. But of course, this is simulation try your best you can get some 20, 30 percent efficiency from this tool or 30 percent you will not reach, but you can try it, but the important thing of this simulation is that you can know the effect of parameters immediately. If you do the 100 microsecond lifetime and do the simulation and do the 1 microsecond lifetime you will immediately know what is the effect. And therefore, it is a very simple tool it is a PC 1D it is a one dimensional tool very fast any computer can run this tool it is free anybody any student can do it and does not take much time once you are used to it it will hardly take half an hour to sit and make any device of your choice very, very nice tool. So, coming back to the surface recombination lesson you need to define how much recombination is taking place and that can be done by the surface recombination lesson. Many of the term actually you might not be aware, but because we have not discussed so less in detail, but in the December workshop everything will go state by state. So, by the time will come to this level you know exactly what is the meaning of SRV and things like that. So, do not worry if you do not it does not make sense to you right now. Then finally, the metal contact. No contact we cannot define it contact is defined only in terms of the resistance that is one dimensional simulation. So, there is no kind of fingers facing another only thing it is saying that we have some contact base contact and end up basically deals with the only in the semiconductor portion. So, contact in PC 1D we can define only in terms of resistance ok or resistivity. Resistance. So, you just define the resistance of the contact at the front and back I think it is one only one context it will just take some resistance only when it will do the simulation right. So, these are the all parameters that you can feed into the simulator is that clear everybody now what are the parameters you need to feed and why you need to feed right. Now, some of these parameters are default parameters. So, like when you say I want to choose p silicon then it will take lot of parameters related to the p silicon end up. So, this is what you need to give to the simulator, but the next question is what you will get out of it right what you will get out of it. The two important thing that you will get out of it is efficiency right. So, you need to you will get efficiency you will get basically I V curve. So, you need you will get I V curve you will get curve something like this right it will give you short circuit current it will give you open circuit voltage it will give you fuel factor it will give you efficiency it will give you series resistance right you that we have given it ok. So, but these are the main parameters that it will actually give it to you it will draw the I V curve for you also it will draw the I V curve for you also. So, suppose now there are lot of lot of study that you can do and people have done earlier and even now they people do it. So, even now you will see lot of not lot, but some research paper which is comes based on the PC 1D simulation international research in the journal. So, one analysis I mean of course, this is very basic enough what you can do is let us say you are starting with the doping of 10 for 16, but you are doing various lifetime of the base ok. So, you can start with the lifetime which may be 1 microsecond 10 microsecond 20 microsecond 100 microsecond do the simulation for all this and what you will see is you will find different different curves you can put them curve together you will find the trained what is the trained of the open circuit voltage as a function of the lifetime or what is the trained of a short circuit current as a function of a lifetime or what is the trained of a efficiency as a function of a lifetime. So, this is one example then you can then you can also vary a surface of commision velocities and plot lot of graphs you can do it you need to just spend some time and you will get. So, this will actually really be useful in understanding what happens if this is the case right. So, the I V curve is one important outcome of it with the another important outcome of this tool is called quantum efficiency. Quantum efficiency is efficiency of quantum normally when I write try to explain the simplest explanation is put the words in it proper perspective ok. So, quantum efficiency of a quantum what is the quantum of energy one photon is one quantum of energy right. So, what each photon is doing in a solar cell is a quantum efficient right for every photon going in how many electrons I am going getting out at best you will get one electron out. So, then your quantum efficiency is 100 percent for each photon there is one electron 100 percent quantum efficiency right. Now, because your photon energy is varying your photon wavelength is varying right your photon wavelength is varying. So, you have to define quantum efficiency for each quantum which means each wavelength ok. So, whenever you what does it mean? So, whenever what it means that whenever you plot quantum efficiency graph it is going to be as a function of wavelength no doubt about that because you are talking about quantum efficiency and the photon wavelength changes photon energy changes. Therefore, efficiency you need to plot efficiency as a function of wavelength is that clear to everybody ok. So, quantum efficiency graph is as a function of wavelength when x axis you put wavelength and y axis what you will put efficiency simple put efficiency, but quantum efficiency what is the best case efficiency 100 percent for each photon if you are getting one electron 100 percent or 0 percent if you are not getting anything 0 percent is the case that you do not want 100 percent is the case that is not possible you will get efficiency in between right ok. So, from where your graph should start at what wavelength your graph should start 300. So, your graph should start let us say 300 nanometer and it should go up to what level depending on the source is of course goes solar spectrum goes up to 400 I am sorry 4000 nanometer 4 micrometer, but when depending on the band gap all the lower energy photons are not absorbed. So, your graph should go up to the band gap energy of the of the material. So, silicon is having 1 point 1.12 electron volt band gap what is the corresponding wavelength calculate, calculate. So, this is the band gap energy of the silicon what is the corresponding wavelength how do we find out E in electron volt is equal to 1.24 divided by lambda in micrometer. So, what we want here we want lambda in micrometer. So, this should be 1.24 divided by E band gap which is 1.12 how much it is 1.24 divided 1.12 1.1 micron or 1100 nanometer. So, your graph for silicon will go up to 1100 nanometer your graph for cadmium telluride solar cell will not go up to 1100 nanometer because at band gap is higher. So, the cutoff will occur earlier your graph for amorphous silicon will not go up to 1100 nanometer because again amorphous silicon band gap is higher and it will cut off earlier right fine. So, your graph will have. So, if I plot this is 0 this is let us say 50 and this is 100 percent your quantum efficiency graph typically looks like and again for various lifetime if you plot this graph for various lifetime 1 microsecond 10 microsecond 20 100 200 you will see immediately difference in the quantum efficiency graph how do you see that. So, this is like a diagnostic tool quantum efficiency tells about what is happening at your surface what is happening at your junction what is happening at your bulk of the material and what is happening at the back side of the solar cell. So, let me draw very quickly. So, I am just putting your solar cell is here light enters from here your emitter is very small your bulk is very thick. So, this part of the quantum efficiency curve tells about what is happening at the back side this part of the quantum efficiency tell what is happening at the front side this part of the quantum efficiency tell what is happening here right. So, that kind of diagnostic. So, your front surface is not well passivated or your surface of commission velocity of the front surface is very high what will happen to the quantum efficiency curve it will not start from 50 it will start from lower value. If your back surface is not passivated it will go all the way down very fast if your life time is very small then this curve will actually go like this. So, this can tell lot about the material itself. So, basically what you are saying each how each photon is performing if you take a photon of 500 nanometer how many of them are successfully getting converted into electron and therefore the quantum efficiency curve is another important curve. Passivation means you specify if somebody is really shouting you specify you know children in foreign countries they use specified if the children is crying they put something specified keep it quiet. So, surface is specified means what if without without surface specification surface is very dangerous it is recombining all the electrons it is hungry of electrons. So, you satisfied hunger by. What exactly. What exactly is done is you put some layer. So, at surface. So, if you look at the crystal you know the atoms are nicely arranged with each other and sharing the bonds and electrons and go to the surface there is sudden disruption and because of disruption some bonds are not made. So, they want electrons and they take electron from all these generated electron. So, they kill them. So, specify them. So, you they want electron basically they want some electron to share the bond. So, you put some hydrogen or something. So, silicon hydrogen bond will make and then you you provide the condition for the bonding and that is what it is. Is that fine? Now, let me stop here otherwise time for simulation will run out of it, but these are the two important thing that you can get out of your simulator I V curve and quantum efficiency curve and all the parameters that you have been defined what you can do now or later. So, this similar will be available. So, may be from 6 o clock in the evening till 12 o clock in the night today you can do all kind of simulation with this computer. It is freeware you can download. So, may be you can give the link which you can download link is already given. So, there are lot of things are possible is the software and as I told there are still some paper which keeps on coming which are in the international journal which are based on the PC 1D simulation. So, lot of things if you are particular thing can actually define and lot of information can be expected. So, I will stop here any questions so far how to define a parameter what parameters are required and how to do it. So, we will tell.